First, please start a new thread (next time) of your own instead of asking a question in someone else'* thread. I split this thread from the one you dug up. When you search, pay attention to the date of threads you read, and don't dig one up that is old. Next, please put your year and trim level car in your signature so we know what kind of car you have every time you post.
Vibration while driving can be caused by a wide variety of problems; axle shafts/joints, bad engine mounts, old struts/shocks, warped rotors, tires, other loose suspension parts like ball joints, tie rod ends, etc.
Because of all the possibilities, it'* rare that we can diagnose a vibration before you check all of these things. Do you notice any noises or vibration while turning the wheels? eg - Bad axle joints may have a clicking noise while turning and can also cause a bumpy ride.
Your trans mount may be an issue.