In order to avoid unnecessary smudges and what not I covered the LCD itself with some plastic wrap while doing the hard drive upgrade. When I reinstalled it all I needed to do was blow off a few dust particles.
I was able to disconnect the two connectors to the front easily. With those off, I just rotated the LCD out of the way to expose the hard drive. Again, make sure it's stabilized if you do this so that when you yank on something else you don't send it flying.
I avoided this step by just flipping the housing over and having it lay flat on the table. The tape on mine was on really tight, and I risking ripping the wires out of the connector if I messed with it (I didn't have some really small scissors which might have helped removing it). I would suggest either securing the body of the iMac and the housing to the table you're working on, or somehow securing the housing to the body, so that it doesn't move around accidentally, since it's only hanging on by a very thin wire at that point.
I didn't do this on my 2133; just pushed wires out of the way.