Help w/ Home Media Server

Could someone please give me advice on the best way to build a Home Media Server? This will be the center of a 3 home computer network throughout a house. Newest and the best Motherboard, cpu, ram and hard drives in some sort of RAID array. I need this to bring in Broadcast, Cable and Satelite TV. Watch one channel while recordering to another. Another computer in the house will be able to watch a channel. At the same time record onto the RAID another channel. Basically act as a HTPC PVR. Also, of course playback DVD's in the DVD drive and play back ripped DVD's off the RAID to other computers on the network.

Software used is:
WinXP Pro sp1
SageTV w/ Sage Client server PVR function
TheatreTek DVD software
Girder
Main Lobby 2, DVD Lobby 2, Music Lobby, WebLobbey
Shrink DVD

Hardware is
Radeon 9700 Pro connected to CRT projector
Haupuage 250 and 350 TV Tuner cards.
Revolution 7.1 audio card.
Vision II case from crtcinema.com (this can support up to 4 harddrives, 1 DVD drive, and 1 floppy)
400 WATT SilentX power supply

I was thinking of having one hard drive as the C: OS and Applications drive. Then the other 3 as a RAID5 arrey.

THoughts anyone?
Your help is greatly appreciated and needed.