EQ2 doesn't have any problems running on dual or quad core machines.
It almost sounds like you're experiencing the problems that the NVIDIA 8800 series users experienced. If you're running one of these cards, make sure you have the latest drivers and try enabling "Reuse Vertex Buffers" under performance settings. If its not related to your video card, then we'll need to do some more digging to find out what could be causing your problems.
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(Rothgar) Re:Intel Processor/Game Performance Need Help!
