My 2000 Passat backed out of the parking space with no problem but when I put it in driver the car wouldn't move....

If you put it in neutral would it roll or are the brakes locked up?

I put it in neutral to push it back in the parking space.

I'm kind of drawing a blank here other than it's probably the transmission. If it's an automatic transmission, have you checked the fluid level lately? The thing is, if the level is low, then something went south so the level got low. I know, not much help.....

ytlas is on the right track it most likely is low on automatic trany fluid. Look under your car for any leaks. Audi trany fluid looks like oil so it can be hard to diagnose a bad trany seal. But conmanly only the rear trany seal will blow ware out and thats where most the fluid goes.