I updated a Mac Mini A1176 1.66 GHz Core Duo with the following:
500GB Seagate Momentus (Amazon)
2.33 GHz T7600 processor (Amazon)
4GB RAM (3GB usable)
New Optical drive (OWC)
New PRAM battery
I found that using one of the old 1GB memory sticks with a new 2GB stick did not work. I had to remove the old stick for the machine to come up. I ordered another new 2GB stick so that I could use 3GB RAM when operating with Lion OS. I know I can update the "bios" to 2,1 and also get Lion operational by deleting the hidden ."pram" file.
I broke one of the plastic post retaining thingys while removing the processor heat sink but fortunately I ordered some replacement plastic screws ahead of time.
Also, I bought the two small bottles of stuff to remove the old thermal paste and I found I had to work away at it several times using a credit card to get the paste of the heat sink and the processor. Also, it was difficult getting the heat sink off the processor after removing the pins. The heat sink was "welded" to the old processor. It came off in the end. The processor upgrade was tricky on this machine. Work slowly and carefully.
The T7600 proc would not "drop" into the socket so I had to apply gentle pressure to persuade it to go in. I was very careful and it locked up ok.
iFixIt has excellent pictures and instructions.