'notebook' and 'desktop' chips are purely made up terms.
Intel even calls the Core Duo a 'desktop' chip.
The difference in Core 2 systems is that the chip marketed toward laptops uses a different socket, and a different front side bus speed than the chip marketed toward desktops.
The 'notebook' "Merom" chip uses the same 479-pin socket used by the "Yonah" Core Duo, and operates at the same front side bus speed of 667 MHz.
The 'desktop' "Conroe" chip uses the same 775-pin socket used by the older Pentium 4 and Pentium D chips, and operates at a front side bus speed of 1066 MHz.
Even though the two chips are based on the exact same core technology, and both are publicly called 'Core 2 Duo', they use different sockets, so you have to make sure you get the 'notebook' chip for your iMac, since it uses the 'notebook' socket and front side bus.
Core 2 Duo produces the exact same amount of heat as Core Duo (according to benchmarks at various hardware review sites around the 'net.)
As long as the iMac firmware supports the Core 2 chip, it should be a simple swap. And since people have done the swap without error, I would hazard a guess that the iMac firmware supports Core 2 just fine.
