There is a free program you can download called AutoHotkey that you can use to automate many tasks in many different ways. One of the things it does very easily is remap keys on the keyboard. You download the program here:
http://www.autohotkey.com/
After you install the program, you can read the documentation built into it to learn how to "program" the remapping of keys. The scripts you create can be "compiled" into .exe files which can then be run at system startup by creating a shortcut in the Startup folder on the Start Menu.
This is a quotation from the builtin help file about remapping keys:
The syntax for the built-in remapping feature is OriginKey:
estinationKey. For example, a script consisting only of the following line would make the "a" key behave like the "b" key:
a::b
The above example does not alter the "b" key itself. The "b" key would continue to send the "b" keystroke