What you need is a Core 2 Duo Intel build and a workstation grade graphics card. The P4C800-E is old technology, socket 478 is long gone and AGP is just about gone. The C2D is outperforming anything in AMD's arsenal right now and is NOT expensive unless you go for the 2 high end models.
I would look at something like an Asus P5B motherboard, E6600 processor, and an ATI FireGL PCI-E video card. 2 gigs of DDR2-667 or -800 ram is the best choice here, get a dual channel kit.
The Antec P180 is a great case. I'd definitely put an Antec power supply in it due to the power supply location and the need for long cables. I'm looking at a similar build for a customer right now, and I'm probably going to be putting an Antec TP II - 550 in it.