Excel 2007 : How to sort data validation menu while typing characters in the cell for the menu?

Hello:

I have come across a new situation after implementing data validation menus. In all the data validation dropdown menus, how do I include the functionality that when I type a part of the name of the item in the list, the item appears sorted in the list. For example, if the item in the dropdown list is "Item1," when I type "Ite" in the cell with the the dropdown list, the list sorts itself to show all the matching items beginning with "Ite" - how do I achieve that? Thank you very much for your help.

Please refer to the attached excel file and some of the menus for titles named "Function Name," "Activity Name," "Who Does This?" and "What Unit Does This?". Pllease also check out the code I have for the whole workbook.