First of all, what kind of car is it?
Also, could you elaborate a little more on the vibration. There are many things that can cause it, flat spots on the tires and balancing problems just to name a few. Does it increase in intensity with speed? How bad is it? Is there just a certain speed range that it occurrs in?
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record