Oh man... i dont feel like typing all that much, first, go Conroe, the cheapest one will BEAT an AMD X2 4800+ and its less than 200 dollars. And the processor is HUGE HUGE HUGE in games!!! Most of us would say Nvidia is a better card, but they both have equals, you can buy equal ATI/Nvidia cards. And if you are gonig to build, wait till after conroe comes out because there will be enormous pricecuts across the board. DDR and DDR2 dont make that much of a difference. As far as PCI-express goes, most motherboards have them now, you wont really have to worry about that. And if you are going with a conroe, you will have to wait to see what motherboards are available at that time. And a conroe, 7800 GT or better, and 1 gig or more of Ram will produce likely more than 80 FPS, and after that you dont need any more really because your eyes cant pick up the extra framerates after that anyhow.
And about wanting to play that one game in the fall, Conroe comes out July, just like you said, which is like 2 months before fall, so i dont see a problem there. And anything conroe will be better for gaming, no doubt about that, the "slowest" one will beat better than almost any X2 processor and anything above the lowest one will beat anything AMD has to dish out or at least be right up there with it. So, if i missed anything clear it up guys, so much for not typing much
EDIT- The conroe is NOT NOT NOT a P4, and yes it will multitask well and be very good for gaming. Anything new with a name like E***** is a conroe and NOT a P4.