Problem in using BIRT

I have recently started using BIRT for some very simple reporting in a Java\Ms Access application. By the logic of the application the user will select a certain database record to view (generally a JComboBox of ID) at this point I want to create a report in BIRT for this ID. I have the basic report design but I can't get a data parameter to work.

I have a Where jobNum = ? in my dataSet SQL and I can set it up to prompt the user to enter the job number but I want to pass the report the job number that is already displayed on the form the user is looking at (it is in a JTextfield).

How can I pass a parameter value to the BIRT report so it only displays the correct record?

Thanks.