I am looking for a socket 478 P4 board. I have a spare prescott CPU, DDR ram, hard drive, case, etc.

I am looking for the most compatible board out there along with a video card for running OSX.

Any suggestions?

There's nothing perfectly compatible with a 478 socket. Your best bet is to find a cheap D915GAVL on eBay and a cheap LGA775 Prescott.

The Asrock P4Dual 915 is about the best for a 478 processor. With Prescott you get SSE3 The built-in GMA900 works well, but slow compared to an AGP card. Search on Asrock P4Dual to see what others have to say.

How about a video card? I haven't had much luck with my x1900xtx in OSX. It works but has some very strange issue.

But if i'm going to build a box just for OSX I can just get another cheap card that is fully compatible.