Private Sub Command1_Click()
Dim xFile$
    xFile = Dir$("c:\Carpeta\*.*", vbArchive)
    Do
        Combo1.AddItem xFile
        xFile = Dir
    Loop While xFile <> ""
End Sub

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Const CB_DIR = &H145
Private Const DDL_ARCHIVE = &H20

Private Sub Command1_Click()
Dim path$
    path = "c:\Carpeta\*.*"
    SendMessage Combo1.hwnd, CB_DIR, DDL_ARCHIVE, ByVal path
End Sub