look on ebay, for windows get a pvr-150, linux get a pvr-200
I use mythtv (linux open source PVR software) with the mythtv XBMC script. This supports live tv(including pausing and time shifting), Recorded programs playback, and Program Guide.
Schedualing of recordings, and commerical skip (myth skips but xbmc does not yet) should be comming eventually. Currently I am using MythWeb (website interface for mythtv) to schedual all my recordings
Now this is not plug and play software. It can be quite a pain in the ass. As long as you are not using SATA drives knopp myth would be your best option. If you dont know you way around a linux console (command line) you are likely going to get stuck really fast.
I have no idea what software for windows works well and has any time shifting, recorded program viewer, or guide.