Declare Function SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd As Long, ByVal Msg As Long, wParam As Any, lParam As Any) As Long
Const WM_CLEAR As Long = &H303
Ну и вызов:
SendMessage text1.hWnd, WM_CLEAR, 0, 0
wParam и lParam не используются (так написано в MSDN)
Помогите, плиз