You need Asus p5k (-C - with support both ddr3 and ddr2, or chip -SE, but you will have only one slot for chassis fun). Or any from P5K.
Why?
1. You gonna get E6850, it supports 1333 FSB, you need mobo which supports the same FSB. P5K does that, p5w does not.
2. This mobo supports DDR2 1066, p5w only 800.