How hard would it be to upgrade from 10.4.8 to any version of Leopard? Thanks =]

It really depends on your hardware. Just backing up your stuff, formatting and installing Leopard would be quite easy if that is what you meant.

Is there no way to do an 'in place' upgrade? I mean without formatting or losing settings

To be honest I've never tried it. What is your hardware? If you're using near vanilla hardware, it might be possible I'm not sure. It would be a lot easier to back everything up and format, but I realize thats not what you're after. Sorry, I really can't help any further than that.

It's gonna mess up the whole darwin bootloader when you upgrade, so you'd have to reinstall darwin/efi/etc so it's probably much better just to do a clean install.

Ah right, well thanks for your advice then =]
How effecient is Carbon Cloner (For making this sort of backup)?