I hope I got the title right this time!

I currently have:

Antec Case w/ 380 watt power supply
A Pioneer DVD RW DVR-06
1 gig of Kingmax DDR 400
Maxtor 80 gig Diamond Max Plus 9 ATA/133
G Force TI4200 (I really don't need any gaming support stuff, on board is fine)

I'd like to replace the MB and Processor with a quad core Intel MB and CPU set, and run a purchased copy of Leopard. I know that the hardware is probably considered ancient, but I'm a grad student and would like to salvage what I can and make a Mac Pro like desktop to run Pro Tools (mixing on my Macbook sucks). I'm amenable to buying additional hardware, but really need to keep this project to $200-$300.

Any advice will be greatly appreciated!!

Nic