First, he'll need some kind of video input for the system. You don't mention what he will be using as his primary source. If he is using a Digital Video camera DV or Digital8, a Firewire port is almost a necessity. You can buy a separate Firewire PCI card or buy a AIW Radeon 8500DV or what I did, buy a SoundBlaster Audigy, which also has a built in Firewire port. Composite, S-Video, and TV inputs are required if he wants to pull video from other sources such as VCRs, TV broadcasts, or non-digital video cams. These can be found on TV cards (many models) and many "All-in-Wonder"-like video cards.
As for video, his GeForce2 GTS will probably be good enough. The Radeon AIW 8500DV would be much better, plus has firewire and all the other inputs, but would add to the cost. He'll have to balance these needs with the cost. Personally, I have a regular Radeon 8500 with an ATI TV Wonder and an Audigy with Firewire port and everything works great.
As for the system itself, any XP 1700+ should be just fine but 512+ MB of RAM is minimum. Don't go with anything less than 512MB. 1GB would be better. For HDD, any relatively late-model 7200 RPM IDE drive will be fine. No need for any kind of RAID setup. Capacity is a different matter. If he is capturing from a DV camera uncompressed, the file sizes will be huge - about 1GB for each 4 minutes of video. I would suggest a dedicated second drive of 80GB minimum. Other compression schemes require less space, but with prices of HDs these days, it makes sense to not skimp on size here.
A good web site to find more info on PC Video is
www.vcdhelp.com. Check it out, lots of interesting stuff here.