Download the source code for the game from http://cubeengine.com/files.php4 and extract the archive. Place the modified client.cpp into the fpsgame directory replacing the old one. Recompile and enjoy.
The game has a terrible habit of crashing when someone joins the lobby you're in. (Don't worry, it isn't that bad.)
The aimbot does not yet work in non-team based gametypes. I'm working on it.
The problem is that you cant actually replace the old client.cpp file because its locked