Well, it's never a good idea to skimp on the motherboard, IMO you would've been fine with a slightly cheaper cpu and a better motherboard, it's easier to upgrade a cpu than have to take nearly everything out to change the motherboard. A motherboard is like the foundation of a pc, and without a decent foundation, expect poorer performance and even lack of compatibility with newer components like pairing the E6750 with an old chipset that has no real native support of conroe.
Nearest to that price with the P35 chipset are
Asus P5K SE Intel P35 (Socket 775) PCI-Express DDR2 Motherboard
Abit IP35-E (Socket 775) PCI-Express DDR2 Motherboard
I reccomend Asus from personal experience, i have never had a problem with them myself. I have heard mixxed views of Abit though, although i have also had an Abit board before and again not had a problem with them either.
Roz