You can get quieter fans at any run-o-the mill electronics/computer store like Best Buy, or Circuit City etc. They're a cinch to install. I think mine were called Alco or something like that. They're about twice as quiet now. (I have 2 fans in my PC.) I still have to put cushions aroun it. I have it jammed in a corner under my desk but it can still breath through the back from an open space above and behind the desk. It's almost dead quiet now.
Some guys go to the trouble to actually build a box/crate to house the computer in and have small holes for all the cords.
Then again, if you're rich you could always by a Mac. Have you heard those little CUBES that are out now? They don't have a fan at all!!! They cool by air induction instead. Can't hear a peep out of em unless you put your ear right up against em. The question is, when are we gonna start seeing PCs with this air inducrion scheme? I'm ready!