I built one from my old desktop components six months ago:
Intel Pentium M 750 1.86GHz
1GB Corsair DDR2 RAM
Nvidia 6600GT passively cooled GPU
400W Tagan semi-silent PSU
I put this in a....
Antec Fusion case
along with...
Samsung 500GB Spinpoint HD
PCI card DVB x2 tuner (x2 tuners allows you to record one channel and watch another) I can't remember the brand off hand!
Wireless mouse and keyboard
Windows XP Media Centre.