I work at a glass and upholstry shop. We use duct tape to hold the windows up while changing motors. But if you use duct tape some of the glue on the back of it always stays on the window and the paint on the top of the door. You just need to use some wax and grease remover (it smells like its mostly made of alcohol) to get it all off with out messing up your paint. i have tried to use masking tape before but the window always slips out of it.

Really the hardest part about doing one by your self the first time first of all figuring out HOW to get all that crap out.( like wich bolts and nuts need to come out and wich ones dont) But if you had to do more than one i would say that the ones that follow will go alot faster. Second getting the window to slip back down into the two holes that hold it in the track so that you can but the bolts in it.

But all in all its a pretty easy thing to do once you have figured it out.