Just set the column count of the combo box to 2. I don't really see what the problem is.
Edit:
Here is a possible workaround. Make the combobox wide enought to display the necessary values in the two columns. Place a label control over the combobox in the position that the second column would be, but make sure that the right hand side of the label control does not overlap the drop down arrow of the combo box. Set the background style property of the label to transparent. Place the following code in the combo box's change event:
Private Sub ComboBox1_Change()
Me.Label1.Caption = Me.ComboBox1.List(Me.ComboBox1.ListIndex, 1)
End Sub