You really don't need a very powerful system. I'd say look into a good capture card with MPEG2 hardware compression and the ability to export whatever it captures as well.
Or, look for a DV-REX. You can find some of these pretty cheap now. I used one on a PII 350 once and it worked fine. The only problem with these is they came out before NTFS was widely spread, so it would automatically start making another video before it hit 2 gigs. I think there are ways around this...
