I am buying a new computer and I decided most of the parts except the case. I am having problems dedicing on the PSU. I find very good cases but most of them are having a power supply at most 350 watts. I am planning to buy the following parts: For the graphic card: ASUS Extreme N6600GT Silencer/HTD, for mobo ASUS P5WD2 Premium, for processer: Intel 3.0GB single core, 1GB RAM, 2 hard drives, one dvd writer, one dvd reader and other small stuff like floppy drive. The case I am looking for will have 2 fans for its own only (other than the ones on the cards) For the case, I am expecting good cooling. Can you help me if I need a 400 watt or 450 watt PSU? And if I need a 400 watt or 450 watt PSU, is it good to replace the PSU in the case with a more powerfull one that I would buy seperatly; may that cause any problem? And lasty, what is the advantage of having a more powerfull PSU than what I need?