Could be the motor that drives the window up and down but more likely to be the lifting gear - often wire cables, pulley wheels and brackets - the wire is the weak link and sometimes breaks.
Need to access the mechanism by removing inner door panel - take off grab handle and any screws underneath. Remove screws from bottom of inner trim panel - will have to crouch down low to see them and lift trim panel off door.
You should now be able to see some of the mechanism - on some cars it's hidden behing a metal plate that needs to be unscrewed.
Peccavi
March 2009