i TOTALLY agree with xxxguitar511, i think this game should be hardcoded, however, I don't know the gamestyle that your aiming for and physic does bring a few unique elements.... i take it you've tried:

-setting your friction to 100
-setting you damping to 100
-using phent_clearvelocity if no keys is pressed

but since this is only a physics box, i think friction alone should do it depending on your movement code