Look into getting an ASUS P5B or preferably a Foxconn MARS Board. The P5B is a tough as nails board, and one of the best
OC boards for LGA 775 out. (As long as you don't need SLI, it is a crossfire board)
Should run you about 80-200 dollars, respectively.
As for a proc look for an Intel Core 2 Duo E6550. Perfect balance of price and performance.