Yes, the USB box or the PCI card in your computer act as complete
satellite receivers.
Just connect the LNB to them, and load the right software.
You will not be able to
subscribe to Dish, DirecTV, BEV, StarChoice, nor Globecast with a card in your computer.
Not in North America.
If you are interested in real Free To Air (FTA) reception (perfectly legal), visit the FTA forum here.
Here's a
handy list of what you might be able to receive.
No HBO, no Discovery, no Speed Channel.... but lots of other good stuff.
You can also get stand-alone receivers, including PVRs (hard disc based recorder) for FTA, too.
Many use external USB hard drives, so connecting the drive to your computer is easy.
Here's an
example from one of our advertizers.
There are other cards and USB receivers for North American analog and digital reception, that work similarly.
PS: I have a StarBox.