P35 chipset does not support SLi, but really at 1280*768, a dual-card solution is pretty pointless, you'd do far better to grab yourself one of ATi's HD4850's or HD4870s which are absolutley great cards for the price, and will wipe the floor with anything below a 9800GTX+ [and above in the case of the 4870] . The absolute best value is probably the 4850 at your resolution.
For a motherboard to put it into, P35 is your best bet [P45 is better for "future-proofing", assuming you planned on getting a bigger monitor one day; though it is more expensive atm, but has the advantage of x8 + x8 crossfire support rather than x16 + x4, which will cripple the second card], although those cards will work in your current board, and right now your graphics card will be the bottleneck in your rig, even if your core2 is low-end.
ASUS make HD48xx cards so if you wanted to get some parts from them, i just browsed their website- not sure if it's the right address to contact them on but you could try that email address listed http://uk.asus.com/aboutasus.aspx?show=3
tell them that you will be posting your build log on several forums, modding the case with ASUS logo's and taking it to your local LAN tournament/computer fair (can't hurt
) I've never applied for sponsorship but i'm assuming it goes something like that? You get the parts and in return they get exposure when you tell everyone how much better their parts are than everyone else's, etc.