No third party tools are needed to do this. It's really rather simple, just takes a couple of moments per VM that you want to resize...I did this very recently for several virtual desktops that needed more drive space for their C drive (persistant VM's)...
Power off the virtual desktop you want to modify.
Open the "Edit Settings" dialog window.
Select the C drive for the VM. Note the path to the VMDK file.
Change it's size to reflect what you need it to be. Close the "Edit Settings" window (use the 'ok' button) and then reopen it again to continue.
Select the VMDK you just resized and select "Remove" for the virtual drive/disk. Make sure you do NOT select to delete the drive, simply remove it from the VM.
Close the "Edit Settings" window.
Open up the settings for a helper VM that has the correct drive controller on it (SCSI should be used, and this shouldn't be an issue) and add the target VMDK to it.
Power on the helper VM.
Once the helper VM is powered up, open a command window and type "Diskpart"
You'll want to enter the following commands:
list disk
select disk n (n is the number of the secondary drive)
list part
select part n (typically 1, but check to make sure)
extend
After a short pause the command prompt should be back. You can type 'list disk' again to make sure it reflects the correct size. If this is the case, power off the helper VM, remove the resized VMDK from it, and attach it back to the original VM.
The longest part of this process is powering on/off the VM's. You can, also, attach several drives to the helper VM to go through many in a single session. Since each VMDK is actually in it's own folder, and you're simply extending the partition to use the extra space, it's harmless (IME).
You can also change the drive size when you P2V a system (or V2V a VM). You'll just need to edit the settings before initiating the conversion. You'll probably want to extend the drive as outlined above, if the OS doesn't see the extended space on power up.
Resizing virtual drives, for Windows prior to version 7 or Server 2008 (might be able to do it in Vista too, but who's actually running that??) is one of the reasons many environments have at least one 'helper' VM available.
I'm sure there are people that use scripts to make all these changes too. I've not needed to do that since I've not needed to do more than a handful of systems at any given time. Typically, if you properly plan out the VM creation, it's not an issue. Most of the time, when converting a physical box, the C drive is resized at that time, making it a non-issue later.
