Sorry about the hardware confusion! I hadn't realized they had a different name before the Intel switch. Also on legality - it's an image that I made in case the original was damaged, in this case being thrown away. Isn't that why we make backups?
SO! The laptop is a Macbook Pro 3,1. The tower is apparently a PowerMac G5 (same case appearance as the Mac Pro).
I am intrigued by the TDM mode of installation because at the moment, this happens:
1) I change the startup disc to the Leopard Install image (I'm actually unsure if it's the opened Image on my desktop or the partitioned and restored image but it boots into it and let's me start the install process).
2) I get to the install and go to select the destination and the External partition ("The Geezy" - get it? ^_^) and it tells me I have to have it as a GUID partition in order to install.
I did find this post -
http://everythingapple.blogspot.com/2007/11/create-leopard-boot-drive-for-powerpc.html - and it appears I've actually done that. I think. I get lost at step 3 though - not enough explanation for me.
So now it sounds like if I can figure out his step 3 or your suggested TDM installation I might get this working?