If your electric windows get a bit juddery or won't move at all give the following a try before resorting to a $tealer!
1. First you need to remove the door card as outlined here:
viewtopic.php?t=11887
2. You will also need some silicon spray for the front window guide and some PTFE spray for the rear window guide. I used these (please don't berate me for having some Rover spray left over from when I had a Metro GTI!)
3. Remove the plastic film protecting the innards of the door then look towards the front and locate the front window guide. Give it a good blast with the silicon spray:
4. Look to the rear, locate the rear window guide and give it a good soaking with the PTFE spray:
5. Wait 5 mins for the lubricants to work their magic then exercise the window. It's probably worth lubing the electric window mechanism whilst you're in there too.
6. Put everything back together and marvel at the smoothness of your windows!
How to resolve sticking/stuck electric windows
There's some more work you can do to free up the window mechanism here too: http://forums.bimmerforums.com/forum/sh ... p?t=709563