We perform the procedure all the time on system and data partitions. As with everything, there are many ways to do it, but this is ours:
1. shut down VM
2. select 'modify settings' in the VIC and change the drive size to 20G
3. fire up VM and extend data partiton with diskpart (will need to download from MS on win2k).
diskpart
list volume
select volume ?
extend
If you need to do this with a system partition, the process is the same except that you'll have to mount the vmdk with a different server and run diskpart from there.
Good luck!
Brent