One that would be born, must first destroy their world...

Should I wait to buy one until the Mac X Leopard version is released?
I wouldn't bother. OS X Leopard is not the major os upgrade that OS X was to OS 9. It will handle some drivers a little better, but if you are just buying a MacBook, instead of trying to build/kluge a mac together, it won't matter. Everything else I have heard of is mostly cosmetic and won't matter much to the experienced computer person.

Is it true that it will be dual bootable (running Mac X and Win XP)?
It is supposed to be. Technically, it is now, but it's such a hastle, it's not worth the effort all but the most dedicated geek.