Try this:
Code:
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
Const WM_CHAR = &H102

Private Sub Command1_Click()
    Call SendMessage(Me.hwnd, WM_CHAR, vbKeyReturn, 0)
End Sub