Decided on the Athlon?
Just a few days ago, I assembled a P4 system with P42.4Ghz and Asus P4PE mobo.
Anyways, don't want this to be a AMD/Intel war zone. So, I'll just recommend on the case. I used an Antec case that came with a 330W Antec Trupower PSU. I must admit since my last session of assembling a system, the cases have come a long way. My last session was about 3 years ago and I used an Enlight case then. It was a pleasure to work with the antec case.