SQL Developer can migrate from Microsoft SQL Server 7.0, 2000, 2005, but, unfortunately, SQL Developer is unable to hande the migration
from SQL Server 2008.
Support for SQL Server 2008 is already planned for a future version, but no date has been yet published.
To migrate your SQL Server database, you will have first to export it and import in a lower, supported version.
I have a migrate of SQL server 2008 to Oracle 11g R2. I think that the option is SQL developer 3.0 (available since March 2011) but i have a problem and questions. Is posible that the migration may be automatically and periodic?
It always better to open a new thread than add to an older one, as it easy to miss.
To migrate from SQL*Server 2005 you can use the SQL*Developer migration workbench.
Full information, documentation, examples are available from these sites -
SQL*Developer main site -
Oracle SQL Developer Migrations: Getting Started -
And if you are looking for a comprehensive guide for migrating databases/applications to Oracle then this book "Migrating to the Cloud" (http://www.syngress.com/information-security-and-system-administrators/Migrating-to-the-Cloud/) can help. I am a co-author of this book.