Thanks for your reply.
Here are some details about my application.
It is a web-based application with the back-end coded in Java and supported by an Oracle Database. The front end is in XUL (a Mozilla technology).
The primary requirement is to try and get a workflow engine to replace the adhoc states that our entities can take based on the choice the user makes. These states are currently just the value of a column in the database rather than a fixed sequence of values (as in a workflow)

Do you think there is a workflow engine that we can customize to fit our application? What we need is an engine that replaces the current states and calls a service based on the state of the workflow at any given point. Also, the workflow needs to be configurable to the maximum extent possible so that the end user can customize/alter it to fit his needs.