Weird...but in the specs it says its x4 so it would really take away performance on your 7900gt.
The gigabyte s3 is probably the lowest budget board you want to get. And if you plan on overclocking, you should get some ddr2 800 ram for the e6600.
CPU: e6600 @ 3.2ghz
RAM: 2GB G.Skill HZ PC6400
Mobo: ASUS P5B Deluxe
GPU: Sapphire HD4870
Soundcard: Creative Labs X-Fi XtremeGamer Fatal1ty
HDDs: 250GB WD + 750GB WD + 2x1TB WD
Monitor: Samsung 226BW
PSU: OCZ GameXStream 600W
Case: Cooler Master Stacker
OS: XP Professional SP3
Mouse/keyboard: Logitech MX518/Saitek Eclipse II
Speakers: Logitech Z-2300