I know plenty of people upgraded their core duo to core 2 duo. Not sure if anybody ever tried a core2 duo to core 2 quad? Sockets look compatible. Not sure if the iMac would recognize it, and if it did, what speed it would set the processor at. I've acquired a late 2006 iMac with a broken display that I plan to use as a small OSX Lion server. I'm not in a hurry to take it apart, but thinking about potential. If nobody can definitively say it WONT work, maybe I'll give it a try some day and take pics. The chips are less than $100 used these days. And I've only got about $100 in the iMac. The time and effort involved with the possibility of it all being futile are the biggest downsides in my mind.