Fat,

Go to Radio Shack and buy a 25 Mh (Millihenry) Choke coil. It looks like a thick wire with micro thin wire wrapped around it. Pull the wire off of the gauge and attach it to the choke coil, and the other end of the choke coil to your gauge. Remember to tape it well. It doesn't matter what side of the gauge you use, or what end of the choke coil (there's no pos or neg end).

How does it work:
A coil of wire will allow battery (DC) voltage to pass freely, but will block any quick increase or decrease in voltage. You gauge will still go up and down and show the proper amount of gas. It will do it slowly, and won't jerk up and down every time you hit a bump.