Anyone, please? 
Does ESX/ESXi put a lot more stress on HDDs, and is the mentioned SSD likely to cope with it?
What is more important for the HDDs, random access time or transfer rate/bandwidth?
Do you run ESX or ESXi on a Dell R300? What are your experiences?
Your help is much appreciated. Thanks!
Hoesi,
I will try to answer all of your questions, if I miss any just ask again!
First let me say this, there is NO REASON why ESXi should not run on the R300. When I said the R300 and R200 were similiar I am referring to raid controllers/nic cards/hard drives/processors. Yes the boards are different, and use different sockets, but these are all on the Whitebox HCL posted here: http://www.vm-help.com/index.html. There isnt any hardware inside the R300 that is totally not supported, with ESXi the biggest components you need to worry about about are the raid controllers, which are SAS6/Perc 6 cards which are used across ALL Poweredge lines, if they work in one, they work in another. The processors should be fine because they are Intel proc's and have good compatiblitly, again they are listed on the Whitebox HCL as working. I would have a hard time believing the R300 would not work with ESXi, as there isn't a single component I can think of that will give you a problem.
As far as SSD's go, I would not use them, personally. Does Dell even sell SSD's with the R300? I wasn't aware of this. I looked on the configuration and the only options are 3.5inch drives, so you can't even go with lower voltage 2.5inch drives. I am not aware of anyone even running ESXi on SSD's, or what vmware's stance is on SSD's, maybe someone else can chime on that.
As far as what is more important regarding hard drives, it comes down to what you are running on the server. Anyone on here will agree that both are important. Fileshare servers that do large transfers are going to need better transfer rate, and a SQL box will need better access times. What kind of raid levels are you planning on doing? You decision comes down to what you are running, 2x 15k 300GB SAS drives are good. I have a PE 1950 with 2x 15k's Raid 1, 1x Quad Proc, 16GB ram and 6 Windows XP VM's doing backend job processes and they run fine. Granted they dont get hit hard in the hard drive area but they run well.
To sum it up, I have a hard time believing ESXi wont run on the R300, I have it installed on NON-HCL Dell hardware working fine, 850's, 860's (w/ P4's! test boxes), DC, Quads not even listed, and they all work fine. You have to remmeber Dell uses alot of the SAME hardware across the board, the 5000 chipset is in the 1950 I believe along with another variant in the 2950, which work fine.
-sixth
Is there any particular (technical) reason to why you would not use an SSD? Dell does not supply them with the servers, at least not standard, but that does not matter. The bays are 3.5 inch, and the disks are 2.5 inch - but that is easily solved with an adapter such as the ICY DOCK MB882SP-1S-1B. The R300 HDD bays are cabled and it won't be a problem anyway, but even with hotswap bays the adapter would fit perfectly. The SSD read/write performance beats S-ATA's by a mile, has no moving parts, less chance of failure, are more energy efficient, and have a very low access time far superior to even the fastest SAS drives. They use the S-ATA interface and, afaik, communicate with the controller like any other S-ATA storage device. Therefore I cannot see any potential compabitility issues here. Do you have anything to suggest otherwise?
It's an application server, and the only disk access will be for the OS (Win 2k3) with pagefiles etc, some minor filebased database stuff, and some basic data logging (maybe 3-4MB per 30 minutes for all the applications in total). No major file downloads or anything like a download server. Probably more like a small database server in terms of disk access.
Anything critical will be stored in databases on separate machines (with redundancy/backups), and the content on the application servers are expendable. Raid for redundancy is therefore not cost effective for my use, and striping is something I want to avoid unless absolutely necessary. (Increases risk of failure, more power usage)
When you've installed on non-supported machines, have you had to follow any particular procedures? I'm limited to working remotely, using a Dell KVMoIP unit - and datacenter remote hands if needed.
Thank you for the help so far, s1xth.
If anyone has first hand experience with ESX/ESXi on the Dell R300's - your input would also be valuable!
I can't think of a reason to why VMWare should have any logical objections to using SSDs for VM local storage. As long as it communicates with the controller as any other S-ATA storage device there would not be any compatibility issues with ESX/ESXi from a hardware perspective. I.e. it would be no different from using any other S-ATA drive, apart from much faster access time, faster read/write speed, and better reliability. If you get a motor or head failure in a spindle based drive - that drive is rendered useless. You also get a complete loss of data unless you send it in for costly recovery. With a SSD drive you have no moving parts and a much smaller chance of failure. If sectors of the flash memory starts to fail over time, the drive will still be usable till you can replace it and you can still recover large portions of the data. So.. With drives using the S-ATA interface/protocol, being faster and having less chance of failure - why would VMWare oppose the use? An even better question is: why should people care as long as there's no technical reason to why it would not function well? 
SSD has not become widespread yet because it is new technology in development, and therefore the high performance drives has been very expensive. The cheaper ones had problems with a very low read/write speed. Companies such as OCZ are now releasing drives with read/write speed of 200/160MB/s and an access time of 0.10ms at a very reasonable price. A 60GB drive at the mentioned spec is just below £200, while a 73GB 15K SAS drive costs £150 + the need for a controller card at around £100. If the SSD drive lives longer, use less power an outperforms the SAS on the areas that matters for your applications - the choice should be pretty simple. I intend to give it a shot, rather than sit and wait for others to make the discoverys for me some time in the future.