My Mac Mini (2007) had become very loud. You could hear the whine from the fan whenever it was running bigger jobs.
I also had tried to upgrade to OSX Lion. When I tried to it said I needed more than the 1GB I had in the the machine. I had some ram handy so I wanted to upgrade from 1GB to 4GB.
The repair went very well. The instructions and pictures were very handy and helped a lot in the disassembly.
I have a couple of things. The tiny black connectors (power I think) are very tight. I had to remove about 3 of them and the tweezers were really not all that helpful. Good strong fingernails were the key.
Also when putting the internal frame back onto the main board of the mac mini, put the 4 screws in place before you drop it down. If you try to put the screws on after you put the the internal frame, you will never get the screws to go into the holes. I tried for 15 minutes to get 1 screw into a hole, until I decided it just would not work. So I took the internal frame back out and dropped the screws in first and that worked fine.
Phillips #00 Screwdriver
1.5" Thin Putty Knife
Intel Mac mini (Model A1176) Fan