Im not sure if this is a dumb thing to ask, But I have been having some bad vibs threw my driveline for a while now and I keep thinking its my driveshaft. But the one thing Im stummped on is, When I have my car in first and both the tires are off the ground, Im still able to spin my tires, Im not sure if this is supposed to happin, But I just wanna know if this could mean something is messed with the gears.

Thanks
Tom

 

So, when you have you car on jacks and in gear the wheels spin. What's wrong with that... Sounds right to me.

 

well I always thought if I have it in gear the wheels wont move, but im not sure if it makes a differance if it is jacked up. Cuz when i spin the wheels the driveshaft stays still.

 

that's normal, the tires should spin in opposite directions when you turn one by hand. If you were to spin both tires in the same direction at the same time, that's when the driveshaft will spin. If the trans is not in gear, then the driveshaft will spin, if the trans is in gear, then spinning the driveshaft means turning the motor.... which is how push starting a car works.
So, with the trans in gear, you and a friend will probably have a hard time spinning both tires in the same direction because you'd also be turning the motor over.