Need help with an AHK script

I don't like that the sprint in MW2 is toggled and there's nothin' in the Option Menu that changes this. I've Googled it and found no solution so I tried to solve this with a AHK script but I failed!
Now I'm kindly asking all you AHK pro's out there if you can lend me a hand and write a short script for me. What I would like this script to do is when I press down Shift, then Shift (or any other button that I can re-map sprint to if necessarily) is pressed down and then immediately released, and when I release Shift, then Shift (or other button) is pressed and released. I basically want to sprint when Shift is pressed and to stop sprintin' when Shift is released.

Thank you for your help!