There are two ways of hacking an RF remote to be controlled by a computer or a microcontroller.
The lame way:
Soldering wires onto the button pads on the remote and hooking them up to an Arduino.
The cool way:
Most RF remotes have a separate module for transmitting data. This device usually has a VCC and a GND line and a DATA line. You can easily transmit your own wireless data by connecting a microcontroller to the DATA line.
However, in order to transmit something that the wireless receivers can understand, you first have to figure out how the wireless data is formatted and transmitted.
To do this hack you will need a logic analyzer and optionally an oscilloscope.
I use the Logic from Saleae. This is an awesome tool and I have done a few reverse engineering hacks using this device!
Check it out at http://www.saleae.com/logic/
It costs 149 USD but it's a good investment for any hacker!
You also need to be familiar and comfortable with microcontrollers and programming in C.