The problem has been reported on a number of different XP machines and one user
on Suse 10, also.

To reproduce the problem.

Setup a HSQLdb server.
Create a Base file, using JDBC to connect to this server. 
Attempt to connect and you are told that the driver can not be loaded.
Go to the Java section of the program options and add the hsqldb.jar, found in
the program/classes directory of the OO.org install into the Class path.
The connection to the HSQLdb server will not work.

Now open any Base file with an embedded HSQLdb database and attempt to open the
tables.
Error; java.lang.NullPointerException

Turning JDBC logging on to FINER yields this in the log:
event no thread   date       time        (class/method:) message
        1 00005904 2007-10-02 19:59:52.75 jdbcBridge: connecting to
URL 'jdbc:hsqldb:C:\Documents and Settings\HP_Owner\My Documents\swarup_base.odb'
        2 00005904 2007-10-02 19:59:52.75 c1: attempting to load
driver class org.hsqldb.jdbcDriver
        3 00005904 2007-10-02 19:59:52.76 c1: success
        4 00005904 2007-10-02 19:59:52.84 c1: JDBC driver did not
provide a JDBC connection
        5 00005904 2007-10-02 19:59:52.84 SQLException to be thrown:
message: 'General error: java.lang.NullPointerException', SQLState:
S1000, ErrorCode: -40
        6 00005904 2007-10-02 19:59:53.87 c1: shutting down connection