Unless you really liked the
Unless you really liked the PC backup of WHS1, I don’t see any reason to switch to WHS2 since it lacks DE.
SageTV doesn’t care what disk your content is on, so you could build any OS you want for the server. Win7 is probably your best bet, but if you had enough ram and a spare license even Vista isn’t that terrible.
The only thing to really think about is whether or not you use firewire channel changing. The driver only works on 32bit systems so Win7 64bit is out if you use firewire channel changing.
Raid depends on whether or not you have content on your server that needs to be protected. The only stuff needing protection on my server is pictures, so there are other options out there for that. I don’t duplicate my videos or movies since I can always just re-rip them.
One thing you might consider in the new build is a SSD for the OS. I’ve heard it really speeds up sageTV even on extenders.