This will help you migrate a Content Database from one SQL server to another SQL Server, on the same Sharepoint instance:

http://technet.microsoft.com/en-us/library/cc288554.aspx (Content DB Only)

http://technet.microsoft.com/en-us/library/cc263299.aspx

http://technet.microsoft.com/en-us/library/cc288019.aspx (Entire Farm)

http://blogs.technet.com/corybu/archive/2007/06/21/sharepoint-site-migration-and-balancing-growth.aspx

Config DB:

http://suguk.org/forums/thread/18132.aspx