Are you using a UserForm or are your controls placed directly on the spreadsheet?
Either way, ActiveX controls (those created from the Control Toolbox) have their own VBA code associated with them. In Design mode, double click the control and VBA will open with:
Private Sub ComboBox1_Change()
End Sub
From there, look at the AddItem Method for populating the combo Box. I.E.
Code:
Private Sub ComboBox1_Click()
With ComboBox1
.AddItem "Office 1"
.AddItem "Office 2"
.AddItem "Office 3"
.AddItem "Office 4"
.AddItem "Office 5"
End With
End Sub
Private Sub ComboBox1_Change()
' Return the selection to the worksheet
Range("B1") = ComboBox1
End Sub
Hope that helps,
Smitty