Dynamic Tables

I have a drop-down box that pulls in departments from a DB. I want the user to
see the information from the department they choose.

For example: A user chooses IT from the drop-down. I want the user to only
see the IT forms appear in a Master Detail Page Set under the drop-down. Then
if they choose another department, they see those forms under the drop down.

Can anyone lead me in the correct direction on how to handle this?? Thanks!