I'm afraid you will have to change the complete logic board. I just fried my MBP's graphic card and this also could not be replaced separately - I had to have the complete logic board replaced.
I own a late 2007 MBPro (3.1) and recently sucessfully upgraded to 6GB by buying a 4GB bar and swapping it with one of the 2GB bars. 6GB is the maximum for this machine afaik. You also have to purchase the right kind of ram because not all 4GB bars will work with the older MBP's.
Hi, I was told not to use fan control with newer versions of SL (I'm on 10.6.8) and Lion because there have been modifications to the fan management in the OS and FanControl can cause problems such as preventing the fans from running faster than 2000rpm and thus making things worse instead of "cool" (: I would suggest uninstalling the app and see if this changes anything...