How Can I Boot to Leopard Disk?

Do you mean, you want to do a fresh install right away and not worry about the initial setup they give you? If so, just pop the disc in, and hold C right when you turn the computer on. But make sure you hold down C before you see the apple logo. But just a little for-warning, if you are booting off the disc's they supplied, they contain all the same software that apple preloaded.

 

And you'll still be presented with all the "first boot" process as well.

Nothing wrong with a clean install, you can eliminate a lot of stuff that will be unnecessary, like language packs, printer drivers, etc., and save gigs of space. As far as the registration & new user setup stuff, it'll always be part of the initial startup process, whether out of the box or as a result of a reinstall.