Customizing the Register New Account Page on JBoss Portal

I am new to Portlets and Jboss.

You need to add a new custom field to the displayed register form. We will need to add a new "UserType" field to capture the user type. The custom type must eventually be stored in the database.

Can you give me directions on how I could do this? What should I learn to accomplish this task?

Modifies the source code for the Jboss portlet required for this requirement?