Bob,
The JDBC drivers work fine for me - using PostgreSQL 8.1.3 and Windows XP. From your error message, it looks like JDBC is on your classpath, which is good. The connection string can be a little finicky. There is a document on the PostgreSQL website that I found helpful in getting my connection to work. Also, there is a JDBC discussion group - it might be better to post there than on this General group.
Good luck!
Michael Schmidt