Indeed. Just plug them into the same router/switch/whatever, and you're good to go. You can share files easily, and even share printers. With a free utility like PuTTY or VNC, you can even log into your Mac from the PC. You are using OS X, aren't you?
The only thing that might trip you up doesn't have to do with the Mac at all...if you're behind a router, it can be kind of a pain in the neck to get a good video chat going. iChat AV seems to do a pretty good job of dealing with firewalls and NAT, but I'm not sure how well other video chat services work.
Of course, if the only reason you're buying a PC is for video chat, why not just tell your friends to use AOL Instant Messenger 5.5? Its video chat feature is compatible with iChat AV 2.1, and you can put the money you'd have used for a PC towards an iSight camera
Which version of the Mac OS are you running? You'll need the latest (10.3) for iChat AV 2.1. Apple sells a version of iChat for $29 that runs on OS 10.2, but that's listed on the site as 2.0, which isn't compatible with AIM.