See my journal http://www.bmwhaus.ie/forum/showthread.php?tid=945&page=2 . I had a similar problem on the passenger side and made a small write up with pictures. There's a small shaft from the motor to the gearbox you need to turn it a few hundred times. Unbolt your passenger seat so you have an idea of what is what.
I stripped the motor down and cleaned the carbon brushes as they were glazed. As HealyC says try replacing the fuse first but if you had could smell the motor burning out I wouldnt hold out much hope.
If you need any more info pm me.