Reinstalling Logic

I've been having some problems with my system drive and it's about time I installed a fresh copy of Logic. I am a registered user, but only have Logic Pro 7 install discs and the Logic Pro 9 upgrade disc.

Does anyone know, can I install from 7 and go straight to the latest version of 9 with these discs?

Does my dongle do all the necessary security/password business? I don't seem to have my original serial number. But, as I say, I AM registered user so that surely won't be a problem...

Please if anyone can guide me through.