expand cells

I was just wondering if anyone out there knows of a way to have a dropdown/select box set to a fixed width i.e. 12.5, but when you open it, the dropdown portion will automatically expand to the largest item in the list, and when you select the item, have the dropdown resize back to the 12.5 size?

The only thing i could find online is

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
If Target.Address = "$D$1" Then
ActiveWindow.Zoom = 120
Else
ActiveWindow.Zoom = 100
End If
End Sub

Which will zoom into the cell when its selected but doesnt expand the cell...

Any ideas??

Thanks