the p5b-vanilla only has one pci-e slot and the p5b-deluxe has 1 pci-e x16 and 1 pci-e x4. The funny thing is its still listed on newegg as having 2 pci-e x16, while the p5b-vm is listed as having a pci-e x16 and a pci-e x4....its a mystery. But none of the p5b series has two pci-e x16 slots.
The asus p5nsli
is prob. your best bet for a c2d with two pci-e x16 (im guessing your wanting to sli???), but don't expect a good ooverclock from that board.
If you can spend $50 more ($250) you would be able to get a p5w-deluxe or a p5n32. They have much better chipsets, if you want to overclock and sli/crossfire that is. p5w = crossfire and p5n32 = sli. (you could run sli on a crossfire mobo and vise versa i believe, correct me if im wrong, but it won't work as well)
Also i think the nforce 600's chipset mobo's are coming out very soon (if their not out already) and they're supposed to be much better, but prob a little over your price.