There should be an uninstaller application in your Utilities folder (/Applications/Utilities/) called either
IntelliPoint UnInstaller.app or
If those are not available, the extensions are saved in
/System/Library/Extensions - namely
MicrosoftKeyboard.kext. In order to safely remove these you will want to run the commands:
sudo kextunload /System/Library/Extensions/MicrosoftMouse.kext
sudo kextunload /System/Library/Extenstions/MicrosoftKeyboard.kext
before dragging the files to your trash. If you don't it may not allow you to delete them until you restart.
/Library/Keyboard Layouts there may be a file called
Microsoft Keyboards.bundle you can drag to the trash and delete as well.
kextunload stands for kernel extension unload.
Credit to Suspicious Package for the details on the installer.