Apple has released Migration Assistant Update for Mac OS X Leopard. it’s a 4.98MB download and requires Mac OS X 10.5.8 or higher.
This update addresses an issue with the Migration Assistant application in Leopard that prevents transfer of your personal data, settings, and compatible applications from a Mac running Leopard to a new Mac running Mac OS X 10.7 “Lion”). You can obtain it via the Software Updates component of the Mac OS X Systems Preferences app.