Richard. I don't think there is any way round the mythtv backend (the part(s) that do the recordings being Linux. There were attempts to write Widows front ends but I don't know the current status. It is suppossed to be uPNP/DLNA compliant so In Theory there a few off the shelf things than aren't mythtv that can view recordings. I think media player on vista can do that?

XBMC or Kodi as it seems to be called no may be an alternative or perhaps work with it. https://en.wikipedia.org/wiki/Kodi_%28software%29

Of course whatever you do, you don't escape some hardware costs and you can't get away from needing a tuner(s). From a Linux perspective, does support a good number incliding cheaper USB dongles but you do need to find out if a particular tuner will work.