It can be done yourself - I've watched a travelling engineer (car lock specialist) repair both my front windows - the mecanism costs about £47 if you shop around.
Remove grab handle (take off cover and undo 2 big screws)
Remove I think 3 screws along bottom of interior trim (will have to crouch down to actually see them)
You can now I think lift off interior door trim by pulling it out at the botom and pushing it upwards (little thump sometimes helps).
All the workings for the windows are hidden behind a metal plate. There are two big rubber plugs - behind them are the clamps for the glass. Undo the clamp screws and lift the glass up and tape it to the top of the door.
The winding motor will probably be OK - undo the screws and put it to one side.
remove the screws for the window mechanism panel (six I think) and take it off. You will probably see broken cable and or broken nylon brackets.
The panel removed carries the door speaker and it's fixed with pop rivets - these will need to be drilled out to get the speaker free.
Rivet the speaker to the new window mechanism and fit the new panel.
Gently lower the glass into the clamps and secure it.
Put the motor back and connect the control switch.
Test the window before replacing the interior trim panel. When you're content it's all ok put the trim back on.
This takes my engineer about an hour and he charges me £50 for his time and callout.
If you do not have a repair manual (£25) and have never done this before expect it to take you about 2 hours or a bit more providing you have access to a big drill and a pop rivet gun.
Alternatively it's about £100 to have an expert do it.
Good luck...
Peccavi
February 2009