Code:
This should get you started:

1. Requirements  2nd form/listbox/command button
   On form2 call the listbox lstDept, the command 
   button cmdReturn
2. A File as source of your departments (c:\departments.txt)
   Assuming there are not a lot of departments and all you
   want is departments I would use a text file. 
'this is the code for Form1

Option Explicit

Private Sub cmdLookUp_Click()
    Form1.Hide
    Form2.Show
End Sub

'this is the code for Form2

Option Explicit

Private Sub cmdReturn_Click()
    Form2.Hide
    Form1.Show
End Sub

Private Sub Form_Load()
On Error GoTo quit:
    Dim myFile As String, myVar As String
    Dim intNum As Integer
    myFile = "C:\departments.txt"
    intNum = FreeFile
    
    Open myFile For Input As intNum
      While Not EOF(intNum)
         Input #intNum, myVar
           lstDept.AddItem myVar
      Wend
      Close #intNum
quit:
  MsgBox "you need to write an error routine for the sub"
End Sub

Private Sub lstDept_Click()
   MsgBox "You have selected " & lstDept.Text
End Sub