I want to rebuild my PC using components that cause the rig to be virtually silent and not noticeably raise the temperature in my home office like it currently does. I've stopped using it because it's so annoying and have been using an old, but quiet laptop instead.

I am not a gamer, so my performance needs aren't very demanding except I need lots of RAM for running VMWare machines (which the laptop can't do),

My current PC is in an Antec Sonata II case, has an Intel 3.0 Ghz Pentium 4 HT 530 CPU (I think this is the main problem) with an enormous Zalman CPU cooler, 3 GM of RAM, Western Digital Raptor drive (its 10,000 RPM contributes to the heat problem, which a SSD HD would eliminate w/o performance degredation), and ATI Radeon X800 XL Video Card. In total, there's 4 fans: 20mm Zalman fans in the back and front of the chasis, the enormous heatsink / fan (the thing's about the diameter of a CD and a couple inches tall) and there's a small fan on the video card.

All of the parts I chose were high performance at the time and consequently, very hot requiring several fans. The Zalman fans, cooler and Sonata case should all reduce the noise, but unlike my laptop, it's still very noticeable when the PC is on. I have read that iMacs are very quiet, but I'd prefer to just keep the cost low by changing out the MB and CPU and maybe even the hot but fast WD Raptor drive. I prefer Asus MBs.