CPUs are no longer measured only by their clock speed (Ghz). Thats why an Athlon 64 CPU working at 2.2Ghz performed better than a Pentium 4 CPU working at 3.0Ghz.
Today however, Intel dominates the market with their new Core 2 Duo CPUs wich are a lot better than even AMD best CPUs - the FX series. They offer much better performance at a much lower price. For instence the lowest end Core 2 Duo, named E6300, clocked at 1.86Ghz is abt as powerfull as AMD's flagship FX-60. The E6300 costs 175$ and the FX-60 costs 800$.
So obviously u want a motherboard with socket 775 for Core 2 Duos. That solves that..
Now onto the rest of the motherboard.
Currently u are looking at two SLi motherboards for nVidia graphics cards, and u can choose beetween ATI and nVidia. If u want to buy an ATI card, u will want to buy a CrossFire motherboard, instead of an SLi.
It depends on how much money u are willing to spend on the graphics card (the graphics card is the ONLY thing that matters). You can either spend 250$ for the ATI X1950XT, 450$ for the nVidia 8800 GTS or 600$ for the nVidia 8800 GTX. If u buy the X1950XT ull want to buy a motherboard that supports CrossFire instead of SLi, for future upgrades - buy a single card now and another one later on when the price comes down, and instead of replacing the card, have them both working together for more value and performance.
CrossFire motherboard -http://www.newegg.com/Product/Product.asp?Item=N82E16813135218
SLi motherboard -
http://www.newegg.com/Product/Product.asp?Item=N82E16813135026