Add Extra Values To A WinForms Combo Box Based On A Hashtable?

I'm trying to add some extra key/value pairs to a combo box using VB.NET. The initial item list is generated from a hashtable, which contains a collection of objects.I've managed to add the extra values to the box using the Add method, however I now run into problems when reading back the selected item from the combo box because some list items are objects, while others are strings.

My best option seems to be to load the initial data as key/value pairs by looping through the hashtable, however this doesn't seem to be working too well either because I'm still getting errors.I'm getting frustrated because it's taking me hours to do something that should take 5 minutes!