Don’t waste your time or money, the easiest way to do it is to is to move your system drive to another virtual guest.
So the procedure is:
1. Shutdown the guest to upgrade (guest1).
2. Shut down the guest (also a 2003 box) you will use to expand the drive (guest2).
3. Using edit on virtual center, add the system drive of guest1 to guest2 as a 2nd drive.
4. Once you added, edit again and change the drive size to your requirements.
5. Turn on guest 2, type DISKPART, LIST VOLUMES, SELECT VOLUME (you want to expand) then EXTEND.
6. Turn of guest 2.
7. Remove the drive from guest2.
8. Turn on Guest 1.
9. Reboot Guest1.
You are done.