How do I reprogram F12 key?

I'm not sure if this is the right forum for it but I want to program my F12 key to tab. I find myself doing a lot of data entry using the numerical keypad on a Microsoft Wireless Comfort Keyboard 1.0A, but because of the lack of a tab key on the right, am forced to be constantly rearranging my paperwork to use my left hand to tab. If I can reprogram the F12 key to tab, it would make my data entry a lot faster and more accurate.

Anyone have a clue as to how I can do this? I'm using Windows XP.

 

Thank you, thank you, thank you, thank you! BTW, did I say thank you?! It works perfectly.