You could use a calculation field with this calculation:
If (JOB ticket::status="New";JOB ticket::_kp_jobticket_id ; "" )
A value list that lists values from this calculation field will only list those that have status = "New", provided that the field is stored and indexed.
For a more sophisticated approach using relationships see these links:
Custom Value List? (What I've described above is "option 1" in this thread.)
http://help.filemaker.com/app/answers/detail/a_id/5833/kw/conditional%20value%20list (a good knowledge base article on the subject.)
Thanks. It works :)