How can you get rid of a game 100 percent off your system you have uninstalled it but theres still some residual files somewhere that tell the game it has been installed on this system before

I can't speak for MacOS or Linux/Unix systems, but here is how to accomplish it on Windows 98/2000/XP/Vista/7:
1.) Open c:/program files/ and search for folders with the name of either the game title or the name of the company that produced it. If any are found, delete these folders.

2.) Go to Start->Run->regedit to open the registry editor. In this step, you must be tremendously cautious, as the registry is sensitive, and a misplaced change to the registry can cripple the system. In the registry keys box (on the left), find the following nodes, and delete any entries with the name of the game title or company who produced it:
HKEY_LOCAL_USERS->Software
HKEY_LOCAL_MACHINE->Software

3.) Reboot your system immediately. If these steps were taken properly, the next install attempt for your game should not be a problem.