10.5/10.4 - transferring iPhoto library

As an avid, but somewhat technically naive, Mac user, why has it proved to be so difficult to transfer my iPhoto library from the backup hard drive of my old Tiger G4 iMac (internal disc failed) to my new Leopard iMac?
I was under the impression that transferring data from 'old to new' would be seamless!
Old G4 was 10.4.11 - iPhoto 5.0.4. New iMac is 10.5.6 - iPhoto 8.0.1
With thanks

I think the problem lies with iPhoto versions.
5.0.4 is very old, and 8 has a lot of features that 5 didn't.
The best way for you to transfer your photo's in this instance would be to burn them to a DVD and then drag and drop the into iPhoto.