This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
You have to make sure that you know about what versions of what products you're talking.
Java 2 Standard Edition version 1.5 has been out since October 2004, so it is as stable as a rock.
Java EE 5 (which you could call "J2EE version 1.5" if you're used to the old names) is still very new and not yet implemented (fully) in the well-known application servers.
Your problem most likely is not caused by a bug in your Java runtime environment, but by a misconfiguration. Put the driver JAR file in the right place. If you have a webapp in a WAR file, you can put it in the WEB-INF/lib directory in your WAR file.