Migration not working

Hi all, im trying to migrate from my old iBook to my new MacBook and im following the steps on screen but it just dont want to work, tried both airport and ethernet cable. My old mac sees the macbook and i put the number in and it just carries on searching until it gives up.

iBook = 10.4.11
MacBook = 10.5.5

does it not work across different OSX versions?
Any other ideas would be welcome.

Thanks