So this looks interesting :)

http://sourceforge.net/cloudscape.php

Hopefully I'll be able to find some time to play around with it...haha finals first i guess...nargh :)

IBM Cloudscape V10.0 is a powerful Java relational database management system that can be embedded in Java programs and used for online transaction processing (OLTP). A platform-independent, small-footprint (2MB) database, Cloudscape V10.0 integrates tightly with any Java-based solution.

Remember to test your Java Foo and win an iPod! ;)