All infrared remote controls have IR emitters (on some remotes you can see them (they look like little light bulbs), on others they are covered by a bit of reddish plastic)
The emitter produces a light (that cannot be seen by the human eye) that light is received by the equipment you are controlling (if you point a remote to a video camera and press a button you will sea a flickering light coming from the remote)
On the T2's RF station there are some holes where you can plug in some emitters.
Emitters come in different strengths and types. some are meant to send a signal all around lick the type of emitters found in remote controls, others are meant to be glued on to your components (such as a TV, VCR...)

Most components use Infrared.

Some components (very high end) have an RS232 port on them, RS232 is a cable that plugs directly into the component (such as a Projector) on one end and on a PC or high end controllers (Creston, AMX...) on the other end. Most of these components can also be controlled by infrared, but the RS232 commands and the IR commands are not always the same.

Dear Daniel & Anthony, thanks for your info. I 've got a much better understanding now.

I think that for most equipment like projector and av controller, the T2 (and even Pronto) should work fine with IR/RF interface. However, I just don't know whether some power amps that do not have an IR interface and just the RS232 or some propriety interface (like something from Mark Levinson) can work with the T2 well.

Just wonder when do you plan to release a file library for the T2?