We have a Craftsman LT1000 Kohler 160HV the belt came off the rear pulley, we were able to get it back on that pulley but the tractor will still not go forward or backward.

I have the same tractor with a 20 hp V twin. Which rear pulley are you talking about, the one that goes to the transaxle from the engine I'd guess? Did you notice a spring loaded pulley that applies tension to the pulley? You must go through that pulley also. I'll check for my manual this evening. Let me know if this is the correct pulley.

Try this site to get a manual for your tractor. You'll need the model number Craftsman Lawn mower Parts, Craftsman riding mower and Craftsman push mower parts
Looks like there are four pulleys in this drive system. At the far ends are the pulley on the engine and at the other end the transaxel pulley. The other two pulleys are close to the engine. One is stationary, just spins. The other is on a spring loaded arm that moves when you push in your clutch. You need to push in the clutch to give yourself room to get the belt over the pulley. I read the instructions and it does not sound fun. You have to be under the tractor on yoiur back. Good luck