Hi djkawther,
Referring to the GWT RPC components, you would define the service interface and its async counterpart for the client-side of your RPC service, and then define the server-side service implementation to actually provide the service. The server-side service implementation is nothing more than a specialized servlet, so as you would use a servlet to interact with data access components talking to whatever flavour of database you are using, so can you use the GWT RPC servlet to interact with these data access components.
GWT RPC components:
http://code.google.com/webtoolkit/documentation/com.google.gwt.doc.DeveloperGuide.RemoteProcedureCalls.html
For more specific details, depending on your use case, as Walden mentioned you may find the Group message search useful as similar topics have been discussed numerous times.
Hope that helps,
-Sumit Chandel
--
Join us at Google's biggest developer event of the year
May 28-29, San Francisco
http://code.google.com/events/io