Looking at setting up a MythTV box (MythTV)
Normal questions - what hardware to get - why can't you get motherboards without inbuilt sound/screen/net etc etc.
Could be fun - so far it may look like
2.x+ GHz processor
2 or 3 250 Gb disks (maybe time to learn lvm?)
Hauppauge 350 encoder/decoder card (1 or 2)
Not sure about graphics card or sound card just yet.
Longer term - add a DVD burner :-)