I own a PB 400/40 GB 5,400 rpm/1 GB RAM running panther.
It still is a sweet machine. Handles everything I ask with dignity. Even my short movies (less than 20 minutes long) or photoshop/illustrator posters and visuals I need to prepare for my research. Again, it is a capable machine. However, I never used VPC and I do not expect performance would be any good.
This is a 4 years old computer than runs OS X panther admirably well, but asking to simulate XP or windows 2000 at the very same time (all systems newer than the computer) may be asking a bit too much.
If you have a windows system though, you can run remote desktop with quite good performance.
good luck