How can triggers be used to change the visibility of custom fields to an user in an given incident.

Actually I wanted the ability to hide and unhide custom fields based on certain fields attributes using triggers. For example, I have a custom drop down menu, and when the users selects a particular category from the drop down, the trigger will hide certain customer fields and unhide others. In our project the user would select which application they are working on, and the trigger would highlight or make visible only those custom fields that pertain to that specific application.

Any ideas? I also called the support line regarding this. Reference 06771823. We kind of need this feature asap. We wanted to go live in Febuary.

Thank you