http://www.ifirobotics.com/rc.shtml#Programming
"2007 RC Code.zip"
You need some program that can open up .c and .h files. MPLAB is the basic IDE (integrated development environment). You can, however, (I think) use notepad. You also need a program to build your "project" into a "hex" file. You also need someone with basic knowledge of C programming. Check out the website for more information.
As much as I don't like IFI right now, they do have a lot of documentation on their site. Go see.
Good luck!
Paul Dennis