Apple released an update of its Migration assistant for Leopard:
This update addresses an issue with the Migration Assistant application in Mac OS X Leopard that prevents transfer of your personal data, settings, and compatible applications from a Mac running Mac OS X Leopard to a new Mac running Mac OS X Lion.
http://support.apple.com/kb/DL1434?viewlocale=en_US
Reminder: Lion is an update of Snow Leopard, so this migration assistant allows you to migrate from 10.5 to 10.7.
