To compile the c code you'll need the mcc18 compiler from Microchip. The evaluation or academic http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en010014|mcc18 should work fine.
After installation, ensure that the mcc "bin" folder is in your path. 'echo %path%' should show something like "...;C:\MCC18\bin;..."
To 'make' use of the 'makefile's set up in each folder, you'll need some form of Make utility installed. For development on Windows, either http://sourceforge.net/projects/unxutils/|Unxutils or Make will work. A single 'make' command in the mergcbus\trunk folder, will build all the individual projects listed in the folder's makefile. When building a subset of the projects, make sure you build CANLIB and CANLDR at least once, if you need to link those libraries.
If you are not using the default PIC18F2480 devices or a standard S1pin location, these are all set up in the makefiles throughout the projects, and you'll need to manually edit them. Be careful not to submit the makefiles back into sourceforge (unless warrented), since it will become the default!
(If you are using MPLAB, you'll need to define or specify S1pin as a compiler directive)
(Also be carefull when using MPLAB, it has a function to generate a "Makefile", which will overwrite the current makefile with a completely different one)