Server 2003 and Virtual PC

I currently own three computers, but only have access to two (one was given to my girlfriend for her use). I would like to learn Server 2003, so here was my plan:
Install Server 2003 on the older PC, then use Virtual PC to create multiple virtual computers on the new PC. If I use Microsoft's Virtual PC, will I be able to network them together and apply AD and GP to them?

Or is it a smarter idea to purchase a new computer for this project?

Yes, you can network virtual PCs with the rest of your network directly if you want. Just make sure you have enough RAM to run the virtual machines.