Upgrade from Tiger to Snow Leopard I have a 2006 MacBook (white, Core Duo) on which the hard disk crashed (it's not even recognized by the system anymore).

I will need to replace the hard disk, possibly with an SSD one, but since I was still running Tiger I figured out it's probably as good a time as any to upgrade that as well.

However, when Snow Leopard was introduced, I seem to remember the cheaper upgrade disk required Leopard to be installed. Nowadays, it seems only that disk is available from Apple, and it doesn't really specify Leopard as a requirement. I don't see a "full install" disk any more (and to be honest I'm not sure I want to pay that price either.)

Did Apple change this requirement because they don't care as much about older versions any longer, or is it still there, but undocumented?

Will I be able to install Snow Leopard from scratch on a new, blank, disk, without having any copy of Leopard whatsoever? Would it be legal?
While Apple stated that Leopard was required to install Snow Leopard, there was no technical limitation put in place. 

From the day it came out Snow Leopard could be installed over top of Tiger or as a clean install. I don't believe Apple has ever released an 'upgrade' OS. The full installs have always been available, at least since OS X.