Correct, the method that requires using MA on both Computers will not work with Tiger/10.4.x
If both of these have Firewire it can be done running only MA on the new Mac & the older one in Target mode...
Then in MA choode from another Disk or such wording.
but this does not work with MacOS 10.8.(2.). In this case the only way is to copy your content yourself from the older harddrive.
An not tested idea is, to migrate via an temporary user over an system between 10.4. and 10.8. But the question is if this makes sense. E.g. the email accounts are not compatible and some more things.