Firstly, all PayTV solutions through MCE require the use of an analogue TV tuner.  This is because it is the AV inputs, not the "aerial" RF input which is used for connection from the PayTV Set top box (usually via SVHS).  These AV inputs are not available to MCE when using Digital cards, even if the Digital card has them fitted, but they can be used by third party applications under Windows, but not in the Media Centre section. 

Unfortunately, Windows Media Centre 2005 does not support the mixing of analogue and digital tv cards, so you cannot use MCE for FTA Digital and PayTV at the same time.