Wu says his sources indicate that external casing changes will likely be modest and that "Apple is in the midst of figuring out whether to power the new iMac with Intel quad-core processors or more high-powered dual-core processors with larger caches." It's almost certain that the next rev of the iMac will have an Nvidia graphics processor. And rumors have swirled for some time that it would sport quad-core processors, at least on the high end machine.

There has also been rumors that Apple planned a 28-inch iMac. Wu said he has expected to see new iMacs introduced at the Macworld Conference & Expo earlier this month. He thinks Apple may be hesitating on quad-core processors for the iMac on fears that the decision could cut into Mac Pro sales.

"While quad-core would provide a material improvement in performance and potentially jumpstart sales, it could cannibalize the Mac Pro, its high-end tower, whose low-end configuration is currently a quad-core," the analyst wrote. "Apple could choose to stick with dual-core on the iMac or make 8-core the new low-end for Mac Pro."

Wu also thinks that Apple may be delaying new iMacs for the launch of Mac OS X Snow Leopard, which will offer better support for multi-core/multi-processors and OpenCL. The analyst thinks new iMacs will arrive sometime between March and June.