You could download this instead: http://homepage.mac.com/shadowboxer/unxutils.exe
which will install automatically.
The program you need is patch.exe, with which you can appy jamp_game2.patch
However, I've just tried it, and it's not co-operating.
Opening up jamp_game2.patch in a text editor, reading through it and making the changes manually may be your best bet if you've already been editing the code.
Grab "Makefile" from Trimbo's universal SDK, and put it in codemp\game
If you have Linux (and if you're a coder and don't have Linux - WHY NOT?
), build your code by booting Linux, changing the directory to codemp/game and entering the command "make".
I've got to go now, but I may return to quarrel with patch.exe later.