Idealy, you'd get a Blue&White G3 Power Mac tower. Jaguar runs on the older beige G3's, but I'm pretty sure Panther is dropping that support. Also, you might check out an iMac, they're pretty cheap and perform decently. I'd look into one of the later models, the ones with the slot loading drives. I have one, and I think they're terrific. Plus, they got airport slots, firewire, and VGA video out, if you want to hook them up to external monitors or projectors.
Personaly though, I'd go for the Power Mac, as its just more expandibly.