Select classification in dialog

I'm trying to get users to select a classification before the main form for an item displays. To do this I have a very simple dialog box with an Item field and a Classification field. This form is connected to the Item Type as a View. In the Item Type client events I launch the dialog box. Everything is good to here. I can select the Item field. It brings up a search grid. When I click the classification field it opens a dialog that is empty. Any clues on how to get the classifications to display for the user to select? Thanks, Brian.