Sharc,
I don't know what kind of GPS your using, but I have an old GPSIII made by Garmin. I bought there handle bar mount(
http://shop.garmin.com/accessory.jsp?sku=010%2D10122%2D00 ) Then put it in a mill and bored the ID out to 1.300 for my ProTapers. Using a thin piece of rubber between the bars and the mount. The mount came with a spring thing that goes between the batteries so the do not lose connection. Works out pretty good, but I do have one problem with it. The batteries do not last very long while riding. I can have it on most of the weekend while walking with it, but only lasts for about 4 hours while riding. I have not figured this one out yet. Oh one more thing, being the inventive person that I am, I also tried to make my own mount out of aluminum. It was a bust. Vibrated the hell out of my GPS and would never stay on. Garmin make a handle bar mount for almost all there GPS's, so if ya got a Garmin, its only about $20 for a mount. Well worth it in my book.
Hope this helps,
Jody