With a $1000 budget I wouldn't get a dual core. Instead I'd spend my money on more RAM and a better video card. Sure the future is dual core but the 3700 will last him through all the upcoming games for a few years and by that time he can upgrade to dual core.
Umm how is it 300 mhz faster? Yea get the 3800 x2 for $330 or w/e it is and you won't be able to get as good of a video card and your games won't run as well. A video card is the most important piece of hardware for gaming. So I say defianately get the athlon 64 3700+ and a good video card.
yea totally the 3700+ because a better graphics card like t he 7800gt over the 6800gs will serve you better than if your gona go dual core. also not many games use dual core right now so you can just upgrade when it does plus dual core will be more mainstream when games do benefit from dual core