I really fail to see what all the fuss is about. If you have a working Intel Mac, and a bootable system disk of a Mac operating system 10.*, then you can instal it on that Mac regardless of what operating system was already there.
Not necessarily so. The hang-ups are Mac model-specific hardware drivers. Because of this, as mentioned before in this thread, you generally cannot install an older version of Mac OS X on a Mac that shipped with a newer one. This doesn't appear to apply to certain current Mac models shipping with Lion, but that's a rare exception.
