I do not play Minecraft or have it installed, but the game info states the sensitivity will be located in a file called options.txt . It says this file is usually in a folder within %appdata% . A shortcut to get into your appdata folder is to open up Run (Press your "windows" key and "r" key at the same time to open Run, Or press Start>All programs>Accessories>Run) and type %appdata% . There should be a options.txt file in a folder within %appdata% probably labeled Minecraft or perhaps Java, and the command to set sensitivity is mouseSensitivity:0.5324
All of this is under the assumption that nothing has been changed since he added Minecraft.
