Since you bought an 8800 GT, your best bet would be an SLI capable motherboard for future upgradability, if running SLI is not a big deal for you, then a motherboard with a P35 chipset would be agood place to start, like the abit IP35 PRO, a really great board (use it myself), and the best thing it allows on the fly overclocking, your CPU, I have seen clocked to over 3 Ghz, so you still got some life life left in that. But if your a hard core gamer, you want the SLI board.

you may want a board that is going to support the new 45nm architecture that is coming out in the next year (CPU)

Other than that a motherboard that supports up to a 1333 Mhz frontside bus, built in SATAII, and legacy IDE (sadly, the IP35 Pro only has one IDE controller, but 6 inside SATAII, and 2 external eSataII, sux for all the old HDD's I have laying around, lol), should support at least 8GB of DDR2 RAM or DDR3 RAM at 1066Mhz or higher.

You can get some more info here:

http://www.tomshardware.com/

and

http://www.motherboards.org/

among others

PS unless that Soundblaster card is a high end one, you wont need it on a lot of newer boards, most support 7.1 HD audio now.

For gaming the dual core will be fine for at least for gaming in the next year, I myself have a quad core Q6600 w/G0 stepping, I have seen it run fine at 3.6 Ghz under load, but long term I believe that the quad core will be useful longer, and:

DO NOT FORGET

you need to have a good MOBO, RAM and a REALLY good GFX card(s) (like the 8800 GT, which itself has a lot of overclocking ability at a good price, and is SLI capable); oh and don't forget a good powersupply, and a well cooled tower too.

you would be well advised to spend some time making sure you have all quality parts that will handle an upgraded CPU down the road, since that is the part that is probably going to be the first to be replaced (especially if you go dual core), if you go quad core you will more likely be replacing a graphics card next.