The q6600 is "for the future" (badly formed sentence) because it has 4 cores which games and programs do not utilize at the moment. Therefore, in the "future" games will use the full potential of the 4 cores thus making 2 core processors obsolete.
If he gets a q6600 then get will have +1-2 years more lifetime with his pc build minus graphics and ram. If he gets the E8400 then he may find himself coming back to tech forums in 2010 wanting a new build that can play Crysis 3 or Duke Nukem Forever. (pun intended)
On that note, if he does not plan to overclock or plans to build a new pc within a few years, the e8400 will be a better buy.