I have a couple of rigs... the server/htpc is a Cel-T 1.2GHz (mega-mega quiet system) and my main rig in an XP 1800+@1938MHz.
IT IS SOOOOOO SLOW!!!
I can't tell you the amount of time I spend waiting around for this to encode, or that to filter, or this to rotate, or these files to copy, or this file to demux... it's infuriating. I have a Ti4400@fast and while it is fine for games (just a light gamer) I often wish it had more grunt when doing CAD/CAM work.
The fastest is never fast enough. It'll always be that way...
Interestingly enough, right now it's the slower of the two PCs that is the most rewarding to fuck about it. Mainly because it looks and sounds seriously good, hehe.