I think the key is what OG-Phantom mentioned: running the installer from an OS that is NOT Snow Leopard results in troubles, I got the same troubles plus errors in the installations log but when I install SL booting from an USB Installer I got none at all, everything works 100% and no installation errors.
So in my opinion the only complete fix could be:
- Installing Snow booting from the DVD/USB.
- Install from Leopard launching OSInstall.mpkg, and then when you have a running Snow, install again from Snow with OSInstall.mpkg, but targeting a new partition.

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AsRock P45TS | C2D E8200 | GeForce 8600GTS
Mac OS X Snow Leopard 10.6.1 + Windows 7 Ultimate 6.1.7600 + Fedora 11