You shouldn't do it that way (transferring a fully-installed bootable disk between two machines, especially dissimilar machines) because it will install different drivers in your new MP than it would have in the old one. After you move the drive it might not even boot.
I just 7-pass wiped my old drive and then installed Snow Leopard from a retail DVD and updated it to 10.6.4 with all relevant software updates.
I also wiped the factory install off the new MP and installed everything except my own user account from scratch. Amazing how much disk space you free up that way, getting rid of useless old apps & library files that have been gathering dust since 2006.
I still have the old MP's original install discs that will go with it in the sale, but who knows what they install. Tiger? No matter, in any event they're only good for booting it for disk utility, not really for installing anything of interest any more.