Accepted Solutions
YES, I have already installed a guest OS (Win XP Pro) in the virtual machine;
Once the OS is installed in the Guest you cannot resize the virtual hard drive smaller only larger. In order to change the size of the virtual hard drive smaller using the Fusion UI and the slider bar under Hard Disks in Settings there cannot be an OS installed. Under that condition (OS installed) you would have to use a different method that would involve creating and smaller virtual hard drive and cloning the existing to the new smaller drive and then switching them out. This can be done with products like Ghost. You can also use VMware Converter to create a new Virtual Machine form the existing one and resize the virtual hard drive in the process.
YES, I do have (more than) one external disk;
That's good because you will need them. 
BUT even after having copied the VM-file to that external disk with 250 GB of free space the changing of the disk-size cannot be performed at all.
You need to be more specific as just saying what you did doesn't really provide any information to give as response to. Have a look as as an example as to what sort of information one should include when asking question.
Since you didn't reply to my post in that thread I have no idea what you did or didn't understand or even what steps you've taken since.
The problem is not that I haven't got enough disk space, but when setting up my Mac which I am daily working with, I partitioned the harddisk (200GB : 31 GB) since I knew that I would need to run Windows in a virtual machine, but I also knew that it would not require more than 25 GB (OS, apps and files).
If you are creating a normal file based Virtual Machine in Fusion that I'm not sure why your creating a separate partition on the physical hard drive as it certainly isn't required and since you haven't mentioned Boot Camp I'm assuming that you just for whatever reason create a separate partition to house the Windows Virtual Machine.
May be it's only me that is confused at this point so I guess I'll just stay out of it and let some others try and figure out what your issue are.
Decreasing a virtual disk in size isn't that well supported. Well known procedures are either by cloning the disks using a third party tool such as ghost or acronis.
Alternatively you might be able to do this with VMware converter, see also
After that you can use vDiskmanager GUI to change the disk format from sparse to pre allocated.
--
Wil
edit: changed wording a bit as "shrinking" is a term used for removing unused space from sparse disks and might be confusing when talking about wanting to decrease the size of a disk.
Hi Stephan,
As you are quite new to the forum, let me explain something about it... not really wanting to be annoying, but probably I will be... 
One of the reason the forum here works so well is because you can assign points to people helping you by using the helpful/correct button when you post back. Using one of those buttons will motivate people to help you out. It's not that important to me (and I'm sure it's not for )
Yet another reason is that by marking posts helpful/correct, it means the value of the posts increase as a lurker can see what has helped.
There used to be some text on the forum here on how it works, but I don't know where that went.
Another reason that the forums work so well is that there's many knowledgeable people answering questions so you can learn quite a bit here.
Anyways, just figured it would be good info to know. Do with the points whatever you like :smileygrin:
--
Wil
YES, I have already installed a guest OS (Win XP Pro) in the virtual machine;
Once the OS is installed in the Guest you cannot resize the virtual hard drive smaller only larger. In order to change the size of the virtual hard drive smaller using the Fusion UI and the slider bar under Hard Disks in Settings there cannot be an OS installed. Under that condition (OS installed) you would have to use a different method that would involve creating and smaller virtual hard drive and cloning the existing to the new smaller drive and then switching them out. This can be done with products like Ghost. You can also use VMware Converter to create a new Virtual Machine form the existing one and resize the virtual hard drive in the process.
YES, I do have (more than) one external disk;
That's good because you will need them.
BUT even after having copied the VM-file to that external disk with 250 GB of free space the changing of the disk-size cannot be performed at all.
You need to be more specific as just saying what you did doesn't really provide any information to give as response to. Have a look as as an example as to what sort of information one should include when asking question.
Since you didn't reply to my post in that thread I have no idea what you did or didn't understand or even what steps you've taken since.
The problem is not that I haven't got enough disk space, but when setting up my Mac which I am daily working with, I partitioned the harddisk (200GB : 31 GB) since I knew that I would need to run Windows in a virtual machine, but I also knew that it would not require more than 25 GB (OS, apps and files).
If you are creating a normal file based Virtual Machine in Fusion that I'm not sure why your creating a separate partition on the physical hard drive as it certainly isn't required and since you haven't mentioned Boot Camp I'm assuming that you just for whatever reason create a separate partition to house the Windows Virtual Machine.
May be it's only me that is confused at this point so I guess I'll just stay out of it and let some others try and figure out what your issue are.
One of the reason the forum here works so well is because you can assign points to people helping you by using the helpful/correct button when you post back. Using one of those buttons will motivate people to help you out. It's not that important to me (and I'm sure it's not for )
We can get points!? Can we trade then for anything? Yes it's nice to get some recognition and points or okay but a thank you does suffice and wila your right the points are not that important to me either and certainly isn't the motivating factor in trying to help people. I do agree that in the sense of a flag it does help others when searching the forum that when things are marked helpful or correct or answered it can help someone that's just not sure feel a bit more confidant that the information their looking at is worth utilizing.
Dear WoodyZ,
thanks for trying to help me solving my so-called problem, and I feel sorry for having sent you into deep confusion .
To get things clearer, let me explain to you that I DID run my Win XP via Boot Camp for about two months prior to having switched to VMware (the erroneous liaison with Parallels shall not be mentioned here ).
Therefore my harddisk was already partitioned and I decided to store the vm-file on that partition (which I, of course, converted from FAT to HFS+ before) instead of reformatting / repartitioning the harddisk and setting up again the faultlessly running Mac OS.
Maybe you (and others) can now understand what my point was when I started the discussion. And having read your answer which I am nor replying to, I think I know what to do and why things did not work like I had expected.
Kind regards
Stephan
(by the way: I always read manuals carefully so as to avoid asking stupid questions ...)
thanks for trying to help me solving my so-called problem, and I feel sorry for having sent you into deep confusion .
JSYK When I said "May be it's only me that is confused at this point so I guess I'll just stay out of it and let some others try and figure out what your issue are." I wasn't really being serious and only expressing my frustration when users just don't post enough information or put things in proper context and was how I was saying until was read and additional information was supplied I just didn't have any more to say.
To get things clearer, let me explain to you that I DID run my Win XP via Boot Camp for about two months prior to having switched to VMware (the erroneous liaison with Parallels shall not be mentioned here
JSYK You can use the Boot Camp Assistant to non-destructively remove the Boot Camp partition to regain that space back to the main partition or boot the Leopard Install DVD and use Disk Utility to preform non-destructive operations. Note: This obviously assumes making the correct choices when doing this. Bottom line never preform disk level operations without having things backed up first.
Maybe you (and others) can now understand what my point was when I started the discussion. And having read your answer which I am nor replying to, I think I know what to do and why things did not work like I had expected.
Yes it's amazing how clear things can be when put into proper context and not to belabor a point however is a good guideline to follow when asking questions.
(by the way: I always read manuals carefully so as to avoid asking stupid questions ...)
Better to ask a stupid question first then to come here after the fact and say I think I did something stupid because I didn't ask first!
Message was edited by: WoodyZ