int pascal CheckMenuItem(HMENU hMenu, WORD idCheckItem, WORD wCheck)  

  This function places a checkmark next to a pulldown menu item, or
removes the checkmark.

Parameters
  hMenu is the handle of the menu which contains the menu item.
  idCheckItem is the identifier or position of the menu item to query.
  wCheck can be a combination or either MF_CHECKED or MF_UNCHECKED and
   MF_BYPOSITION or MF_BYCOMMAND.

Returns
  Nothing.

Example
  CheckMenuItem(GetMenu(hWndMain), ID_BOLD, MF_BYCOMMAND | MF_CHECKED);