VPC works ok with Windows2000, but since you're getting the bundle, I think they make you go with XP. Just turn off all uneccessary services. It will be slower than your PC, but for basic stuff, it isn't that bad. Since you're keeping the PC around anyway, you can run Remote Desktop from your Mac to it, and it will be faster. If you can afford the 1GB from Apple, go ahead and get it. OS X doesn't eat RAM, but it will use as much as you give it. The more you do, the better it will be to have as much RAM as possible. The Mini is no speed demon, but it's no slouch either.
The only killer might be the slower hard drive. But if you don't mind notebooks, it will be about the same. You might have been better off with an iBook, or PowerBook though.