I faced the same decision when building my 15 year old nephew a rig. I ended up going AM2 4600+ and paired it up with an 8800GT. Doing most tasks that my nephew does I am never able to tell the difference between his 4600+ and my Q6600. Honestly the only differences I see between my AM2 and my Intel setups is folding and benchmarks. I don't run FRAPS or anything like that when I game so as long as it looks good and doesn't drop frames I'm pretty happy..
My recommendation, if he plays games is to choose the vid card and
PSU first, then pick the rest of the parts..