I'm going to assume you have a vba Userform which is where the ComboBox2 and Textbox1 objects are sitting. The code should be located in that object (the userform itself).
In that userform you will need two macros that autoexecute (run when events happen that align with the name of the macro). So add this code to the userform module.
Code:
Private Sub UserForm_Initialize()
Dim depts() As String
depts = Split("Accounting|Maintenance|Commissary|Sales|Field Reps", "|")
Me.ComboBox2.List = depts
End Sub
Private Sub ComboBox2_Change()
Dim people() As String
people = Split("Mary Smith|Fred Jones|Jose Lima|Rick Nixon|Sandy Banning", "|")
If ComboBox2.ListIndex = -1 Then
Me.TextBox1 = ""
Else
Me.TextBox1 = people(ComboBox2.ListIndex)
End If
End Sub