Place window relative to parent
//hWnd is the parent window
hwndStatusBox = CreateDialog(hInst, MAKEINTRESOURCE(IDD_STATUSBOX),
                             hWnd, svnStatusBoxProc);

SetWindowPos(hwndStatusBox,NULL, 100, 100, 0, 0,
             SWP_SHOWWINDOW | SWP_NOSIZE | SWP_NOZORDER);

ClientToScreen

message_box_position = {ParentWidth - MessageBoxWidth, ParentHeight - MessageBoxHeight}
ClientToScreen (parent_window_handle, &message_box_position)
SetWindowPos (message_box_handle, messahe_box_position)