I faced the same problem using MySQL schema. I found the solution at http://www.jboss.org/wiki/Wiki.jsp?page=JbpmWiki, you'll find a valid mysql schema attached to this page, I know you're using postgresql, however mysql's schema could be helpful.
Yes, there are no semicolons at the end of the line, but no big deal:
postgres> cat jbpm.jpdl.postgresql.sql | while read line; do echo "$line;" | psql jbpm; done. While the creation, the database complains about nonexistent tables, but the script goes on, and eventually creates the required structure. I use PostgreSQL 8.1.4.
Thanks for the example, I used something similar myself ;)
I don't run plsql in auto-commit mode, so I wrapped the script with BEGIN/COMMIT - but as soon as you get an error inside a transaction you have to roll back, hence removing the drop statements.
It's nice to know that there are other people using PostgreSQL (I'm on 8.2).