They switched to Intel because IBM was dropping the ball on future development for the PowerPC architecture. As for why they picked Intel over AMD, I have no idea.
At any rate, the new Macs are the first computers to use Intel's new dual core processors. Gives a pretty dramatic speed boost. Apparently the new laptop is the fastest laptop on the market (for the next few months, until other companies start shipping laptops with the Core Duo in them).
And yes, one could dual boot XP (or run it in a virtual machine), but why would one want to do that? *shudders*
Anyway, none of this is relevant to my question. My guess is that it will be simple to recompile the tarball to run on the x86 version of OS X, but I was curious to know what taylor had to say.