I have an early 2008 iMac and it was running a little slow. It's a great machine and I wanted to find a way to speed it up. I read about replacing my HDD with a SSD and watched your video (iMac Intel 20" EMC 2133 und 2210 Festplatten-Austausch). It looked pretty easy and I decided to give it a try.
Everything went well and exactly as shown in the video except for one thing. When I got to the point of removing the LCD, the video shows that you unplug two cables. I had a really hard time finding one of them since there was nothing in the area that looked like it could be removed without unscrewing something. After gently trying to lift the LCD, I saw the second cable and it was something that needed to be unscrewed. So, the video is a little different in that regard. The biggest problem I had is not shown in the video since it is about replacing a HDD with a bigger one. My problem was fitting the new SSD into the HDD space. The 3.5 inch adaptor for the new SSD is just way to small to get it anchored in place where the HDD was. There was no way (absolutely no way) it was going to fit. After trying several ideas, I ultimately ended up using strong double-sided tape to secure it. I think it will work. And, if it comes loose, it doesn't really have anywhere to go anyway. It's in a tight space and can't move much. I also never move the machine around so there isn't going to be anything that will jar it loose. The machine works beautifully with the new SSD. I run Mountain Lion and bought an OCZ Vertex 4 256 GB. The machine is so fast I can't believe it!
--Remember to hook up the temperature sensor to the new SSD (and tape it down). I've read about a lot of people having problems with the fan.
--Remember to enable TRIM.
--Look around and see if you can find a 3.5 inch adaptor that is designed to fit in the space of your HDD. Otherwise, come up with a method of securing the new SSD.
--This isn't a hard job with a 2008 iMac!