Htpc is my main interest in pc. I've built over 70 rigs now, and made a bit of pocket money from it!
I used to have that card! you can indeed get a firewire pci card. I would recommend a card that has some internal firewire connectors.
Do you have the separate CI add-on. I would thoroughly recommend it as the module in the card makes the card too not IMO. But if you can ventilate the card you may be able to control this.
Also , what program will you be using to view channels? I recommend dvb viewer, though the ('Fire dtv' app they include is a decent lite version of this).
Even though vista media center(in vista home prem and ulti)can support dvbs with the recently leaked update, it doesn't support CI.
Dvbs2 isn't supported in media center as it has no certified mpeg4 decoder; so best to stick with the other apps for this. Of course, theres not many dvbs2 channels atm anyway.
If youre plugging into a tv, media portal gives you a media center type interface thats great to navigate if you have an appropriate remote.
Let us know if you need any extra pointers with your setup.