The difficult I do immediately, the impossible takes a little bit longer.
For those that prefer a Drop Down, like those found on Web pages, as opposed to a Combo Box...
Option Compare Database
Option Explicit

Private Sub lstListBox_AfterUpdate()
     Me.lstListBox.Visible = False
     Me.lstListBox.RowSource = "SELECT [tblClientProfile].[cpClientID], [tblClientProfile].[cpCompanyName] FROM tblClientProfile;"
     Me.cmdSelectCompany.Caption = Me.lstListBox.Column(1)
End Sub

Private Sub cmdSelectCompany_Click()
If Me.lstListBox.Visible = True Then
     Me.lstListBox.Visible = False
     Me.lstListBox.Visible = True
End If
End Sub

Private Sub Form_Current()
     Me.lstListBox.Visible = False
End Sub
After *selection* from the list the Command Button will change to the Company Name.
The Code...
Simulate a Drop Down Box...
Download Sample  (Access 2007 and higher)
Make Controls resize with a form  (Access 2007 and higher)
Switch Windows  (Access 2007 and higher)
9.11.2011 - Fixed *94 Invalid use with NULL* error when run in Access 2007