Unlike Core Duo, which is packaged for Socket 479 (as will the future Merom), Core 2 Duo is packaged for the LGA775 socket which is used by current generation of Pentium 4/D. It was designed from the outlay to be a drop in replacement making upgrading easy. This socket compatibility also meant plenty of motherboards already available on the market at launch date. Below, you can see the Core 2 Duo and Pentium D at the very top which look so similar that I'm not even sure which is which.
At the bottom is Socket 478 on the left with a Pentium 4 and Socket 479 on the right, with a Pentium M. Notice how similar the Pentium M is to the much older Pentium 3 with its capless design.
If you've not dealt with LGA775 before, you'll notice above that the pins have been removed and instead placed on the motherboard itself. These are far more sensitive to being poked than the traditional pins on the back of a CPU, as I recently discovered to my misfortune.
Intel obviously put a lot of work in to reducing memory latency, while AMD took the much simpler (and in my opinion more elegant) approach of just putting the memory controller on the die. If Intel could be accused of anything it would be of over-engineering.
In theory, Core 2 Duo should work in any 945/955/975 chipset motherboard. If this plan had executed smoothly then Intel's over-engineering could be forgiven as for once Intel wanted to make sure we weren't forced to shell out for new kit (shock horror!).
Unfortunately, as with many things, it didn't work out quite as well as planned. Many LGA775 motherboards are and never will be compatible with Conroe. Most will need a BIOS update. This sounds simple enough, but if you buy a board from a reseller that doesn't have a recent BIOS on it (perhaps older stock), you'll need a second pre-Conroe processor to be able to update the BIOS. However, the best example of this blunder is the fact that even Intel's own 975 desktop motherboard won't work with Conroe (unless you are prepared to do some rather fiddly soldering) and a new revision had to be issued.
Although Intel's intentions are noble, it is unfortunate to see this happen – for both the consumer as well as Intel. But I am not mentioning this merely to poke fun at Intel's attempt, but rather as a warning to be doubly careful when choosing a motherboard.