I had some trouble getting PostgreSQL up as a Websphere v5 datasource.
When I did some searching, I found a lot of other people who had
problems, but no one had the solutions. I even ran into a few posts
saying it couldn't work until there was XADataSource support in the
Postgres JDBC driver.
We I was finally able to get it to work. To save the next guy some
grief, I documented it here....
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=46&t=007563