I'm about as bad off as you are (as far as hardware), but I don't run that hot. I've got a P4 3.2GHz with an aluminim case, 1 HDD, 4 sticks of RAM, and an x700 PRO all trying to run off a 305W psu. I've got a Dell, so its a pain to upgrade.
I have just got a new aluminum case that included a 400w psu. I got a p4 3.2 ghz that runs at 90oF, under extreame gaming load 125oF, with the radeon x800 pro, 1 hdd, 4 sticks of ram. Check it out at newegg. http://www.newegg.com/app/Showimage.asp?image=11-146-007-01.jpg/11-146-007-15.jpg/11-146-007-32.jpg/11-146-007-33.jpg/11-146-007-16.jpg/11-146-007-11.jpg/11-146-007-34.jpg/11-146-007-35.jpg/11-146-007-36.jpg/11-146-007-37.jpg/11-146-007-12.jpg/11-146-007-13.jpg/11-146-007-14.jpg&CurImage=11-146-007-01.jpg