On Linux, all that's really needed is a configurable call-out from SageTV: the ability for SageTV to call out to a user/vendor supplied script to schedule a shutdown/wakeup sequence.

With that, anything is possible, and not at all difficult.

On the Windows side, the impression I got from the SageTV site/forums, was that normal windows power management could be used to shut the machine down when idle. SageTV prevents the maching from appearing "idle" when it is busy recording/playing. There were no details about when/how it sets the wakeup alarm, though.

Cheers