You should mark it when you take it off to ensure you put it back on right, but with a 20 year old car there's no telling if it's been taken off and put back on correctly before.
But, there shouldn't be any vibration from it. If the driveshaft has some counterweights, you might experience some vibration. But since the driveshaft is from another car, if it does have some counterweighting, it probably won't be a good thing since it was balanced for another car.
If you do experience vibration, just try rotating the driveshaft until it stops, or if it doesn't, you now have an extra special characteristic in your car.