It could be that your G4 Mac cannot read the disk due to the partitioning style the new Intels use. GUID versus the old powerpc style.
If that is the case, connect the disk to to Intel Macbook and connect both Macbooks together with an Ethernet cable. Share the disk on the Intel Macbook, open it on the G4. Should function in the same way as a directly attached drive from there on.
if you have an external USB case you can chuck the G4 drive in there and then just create a dummy admin account on the new macbook... from there you run the Migration Assistant and choose from a time machine backup another disk, then you just choose your external disk and pick your user account. It will transfer everything including all your apps etc! it really is a pretty awesome tool and lightyears ahead of the crappy windows file and transfer wizard!!!
