I have exactly the same question. Some explanation would be great ...
I have posted an example of how to do this with Oracle 11g Express at the following location - note this will assume you have the H2 installation working as described in a related post.
For Oracle 10g - If using Express you will probably find that this example will work as is - maybe a slightly different Oracle JDBC driver version required.
For non express Oracle - assuming you have granted create database privileges to your user - all should work fine.
I think though from a best practices point of view it is probably better to continue the pattern set by express and create the target database independently in the instance, and grant only the object creation rights to the user.