Ok, since your general limit is around 250 per part, I'd suggest you drop the very most on your GPU. How bout a nice
Albatron nVIDIA GeForce 6800 GT Video Card, 256MB GDDR3, 256-Bit, TV-Out/DVI, 8X AGP, Model "6800GT" - RETAIL - $399? Then you can use coolbits to OC this card to the 6800 Ultra's core/mem speeds with almost 0% increase in heat. I'd definitely drop the most in this, especially for Doom3.
You could probably drop that 160 GB Samsung and hit up a 74GB
Raptor for $156.
About RAM: You're gonna be limited to PC3200 on this, because that's the max the board can handle. In this situation I'd suggest the
Corsair XMS Extreme Memory Speed Series 184 Pin 512MB DDR PC-3200C2PT - $114. Overall, some really good RAM, and you can get 2 strips for under $250
.