Well if you're trying to future proof this computer , I'd go with a quad core, such as Q6700, if you can manage to fit that in your budget. Otherwise you can get the Q6600 and overclock it
Again, if you want to future proof, you'd want to go with a P35 motherboard, otherwise go with something like Asus P5B-Plus or Asus P5B Deluxe.
For the graphics card, I would go with the 8800gtx. Don't go with two lower cards in SLI, because that doesn't get much performance increase over a single card...plus the power requirements are nasty for SLI.
I would also suggest 2Gb of ram..such as these.