It's a mouse fix that proffesional gamers use for accurate mouse sensitivity.
One of the Cyberathlete Professional League's members' have made this simple 
registry change that will disable any mouse acceleration made by Windows XP. 

Be warned: it will feel akward and slow at first. This is true. By removing 
acceleration, your mouse pointer, (crosshair perhaps), will accurately display 
the movement that you make on your mouse. Therefore, making a very-sensitive mouse 
movement. It may not have any effects out-of-game, but it is VERY noticeable ingame.

It maybe wierd at first, but hell, once you get used to it, it may improve your aiming skills.

Installation Instructions:
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1) Open the RAR file, and execute the Registration Entry File.
3) Select "Yes" when prompted.
2) Restart your computer.

Uninstallation Instructions:
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1) Open the RAR file, and execute the Registration Entry File.
3) Select "Yes" when prompted.
2) Restart your computer.