PII with 128MB RAM is the bare minimum to word process, e-mail, and surf under Windows 2000. Under XP I would up that to a PIII500 with 256MB RAM.
For modern games, my Athlon 900 TBird with a 128MB GeForce Ti4200 and 384MB RAM under Win 2000 is plenty fast to run things. But within the year it will probably not be enough to run modern games.
The bottom line is, if he only want to e-mail, surf the WWW, and word process, reload the OS on his current machine and give it the virtual enema. If it is for games, go with a Athlon XP Barton 2500+ and a decent motherboard, 512MB RAM and upgrade him.