For information and reference guides on how to migrate from SQL Server to Oracle, visit Oracle Technology Network's Migration Technology Center. This section of OTN contains extensive information on how to migrate your data from SQL Server (and other platforms) to Oracle. From this site, there is a link provided to the migration workbench.
In addition, Oracle provides a data migration verifier that will assist you with your migration to Oracle. This verifier can be found here.
I have not used the migration workbench so I cannot offer advice on what its advantages or disadvantages might be, but it definitely looks to be worth a try.
This was first published in January 2006