Quad-core compatible motherboards

All of Intel's quad-core CPUs use the LGA775 socket, which dual-core chips and even the older Pentium 4's used.

However, there are a number of other factors that determine whether a board will support a particular quad-core chip.

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The first factor is the board's core-logic chipset. This acts as a high-speed electrical interconnect that allows every component and peripheral connected to your machine to communicate with each other.

Most of the chipsets released in the last year and a half support quad-core processors, though there is an exception. Intel's recently-released 1333MHz FSB 45nm Penryn-based quad-core model, the Intel Core 2 Extreme QX9650, is only compatible thus far with Intel's own X38 and P35 chipsets.
Certain boards using the older 975X and P965 chipsets may also be compatible if they are newer revisions with the updated Penryn-compliant circuitry and BIOS.

65nm quad-core CPUs, such as the Q6600 are compatible with all the core-logic chipsets released in the last 18 months.

All of these chipsets support the 1066MHz FSB, the lowest frequency that quad-core chips use, as well as either DDR2 or DDR3 RAM. Note: If you have a flexible budget, a more expensive DDR3 motherboard will make more sense in the long run as DDR3 memory will eventually replace DDR2 as the dominant RAM.

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Besides the chipset, the next factor determining whether your motherboard can dance with a quad-core processor is its Voltage Regulator Module (VRM) circuitry. Such circuits are responsible for supplying your processor with the juice it requires to function.