Those receivers that have a CI (common interface) slot can take a CAM (conditional access module) that will enable you to view, with a suitable card, those channels encrypted by the service provider (e.g. D+, TPS etc.)
Certain kinds of CAM. e.g. Magic, Matrix are programmable, either as they stand, or with cards that are themselves programmable.
For a good tutorial on CAMS and programmers, see
http://www.duwgati.com/uk/index.htm
As for channels openable with a patched receiver, the above service providers and some others are at present compromised. I suggest, when you obtain a suitable receiver, check yourself what is in the clear, as openings can change from time to time.
Encrypted S*y channels cannot be viewed with a patched Fortec receiver.
You really need another, larger dish pointed at, say, Hotbird (13E) or Hispasat (30W) to take advantage of the channels the patched box can open. Or go for a motorised dish.
Llew