I had an ATI video card originally which worked fine with DVB-S but had the common green/blocky problem with DVB-T.
So I switched to a 9600gt, now my DVB-T is fine but DVB-S is unwatchable. It is sort of pixelated and scrambled with the sound cutting out every second or 2.
I have all the latest drivers from nvidia and for my tv card and have even gone so far as reinstalling the OS.
I use a 360 as an extender on another TV and the DVB-S channels work fine.
Does anyone have any ideas on other things I could check?