As I have already said, I don't recommend building a PC unless you have a really good reason... one good reason to build or modify a PC is to make it quiet, particularly if it is a home PC. QuietPC supply many many components that are engineered to be quieter as well as cases and acoustic kits that absorb the sound that is enevitable made. Definately worth a visit. I have a server that runs 24x7 (doh) and it doesn't wake the kids...
If you do have a really good reason to build a PC and you know how to do it you'll know where to get the bits so I'm not going to suggest anywhere else here...


