Are you trying to connect to an external database? Since 4.2, you have two ways to do that:
1. Accessing a Linked Server from Integration Studio
2. Accessing a Database Connection from Integration Studio
You can read the following help about Integration Studio that explains the steps to be followed:
Check this video http://www.outsystems.com/networkforums/ViewPost.aspx?PostId=12166, specifically timeframe [5:43 – 10:06], which deals with the configuration of a Database Connection in Service Center and its use via Integration Studio.
Regarding your specific case, you may not see the tables if permissions are not covered for that database. Check out the reply to http://www.outsystems.com/networkforums/viewtopic.aspx?topic=external-table-importation---outsystems-plataform-4.1
Let me know if this helped.