You might end up waiting for a long time. You’ll find out in less than a month what processor the G5 PowerMac replacement will be (like the Mac Pro) in terms of processor. If Woodcrest makes it into the Mac Pro, you might see a revision of the iMac in time for Xmas to have Conroe (the Core 2 Duo) in the iMac. This may be the case because Core 2 Duo currently will not allow multiple processors (aside of the cores that is), and since it’s likely that Mac Pro will have a top end “Quad” machine again, you’ve got a chance. -BUT, the issue is that the first line of Mac Pros might be Conroes and a ‘Big’ machine will come out later in the year, in which case a Core 2 Duo revision would not come for iMac simply because it would not allow the Mac Pro to be a bigger horsepower jump.
Anyway, Core 2 Duos will certainly come out in the iMac, but I think it will be late in the year, maybe even first quarter again. But then, I just read a lot, I don’t know anyone on the inside.