A good choice for a tv tuner to use with Casema would be the FloppyDTV together with AlphaCrypt works great!
To get other ideas for your setup you should view my setup (in my signature below) because it's very similar..
Also for what you want (from what I can read in your post) you don't need the extra gfx card as the onboard gpu is more then enough for HD, unless you are planning to play games than it would make more sense to have the extra power
