This is just something I whipped up for a person project and I thought you guys might find it useful.
All this app does is simulate a keyboard key press of your choosing when the guide button is pressed on a 360 controller, allowing you to actually use the button for something.
It's a simple little systemtray app, there's next to no configuration and for the time being I'm not even going to put it on my site... I'll just attach it here. Have fun!
Note that it does NOT work in mame because mame just can't handle simulated keypresses BUT you could use a key2joy program in conjunction with this like ppjoy and that would work in mame as simulated joysticks work just fine.