This happens when you find install Ubuntu on vwmare and then find that the partition is too small for root.
Belows are what I do to solve this:
1. try use vdiskmanager to resize the vmdisk file
http://www.vmware.com/support/ws45/doc/disks_vdiskmanager_ws.html
2. Download the iso of live CD of gParted
http://gparted.sourceforge.net/livecd.php
3. Set the CD connected at the startup at the VMWare Workstation preferences
and set the source as the iso
4. Start ubuntu, press F2 and change the boot sequence.
Press "+" over CD to make it booted first.
5. After entering the interface, resize the boot.
If the unallocated partition is at the end, it needs to be move till close to the root partition and then resize the root partition.
BTW, Ubuntu 10 has come out. Go and check the new fancy stuffs.