The migration module is included in the latest 4.2 release of Sitefinity. However, it is currently in a beta state at the moment, and supports importing content from Sitefinity sites running version 3.7 SP4 Standard Edition.
An upgrade guide for moving from 3.6 to the latest 3.7 is available here: http://www.sitefinity.com/devnet/upgrade-instructions.aspx
Currently you need to be running the asp.net 4.0 version of Sitefinity 3.7 to migrate, however the team is working to add support for sites that are on asp.net 3.5.
There is also a guide available: Sitefinity 3.x to 4 Migration Guide
that will be updated as the Mirgration Module continues to improve.
Let me know if you have additional questions, and I hope you will share your feedback with us.
hope this is helpful!