Does anyone know of a good Linux distro with a kernel that supports dual cores?
Erm, any 2.0 (or better) Linux kernal will support Symmetrical Multi-Processing (aka. Dual Core CPUs), if configured correctly. Most distros will include SMP enabled pre-compiled kernels. Or better yet a way to load Mac OS on a regular PC?
From what I understand you need particular Intel motherboards that supports EFI. Other than that Intel MacOS X should work out-of-the-box, providing you can find the correct drivers. there is absolutely no technical reason why it couldn't run on a stock Dell machine
Apart from "Dell machines still use archaic BIOS architecture", then no.