function addOpt(oCntrl, iPos, sTxt, sVal){
     var selOpcion=new Option(sTxt, sVal);
     eval(oCntrl.options[iPos]=selOpcion);
   }

   function cambiar(oCntrl){
    while (oCntrl.length) oCntrl.remove(0);
    switch (document.book.Course.selectedIndex){
     case 0:  
      addOpt(oCntrl,  0, "2 Weeks", "2 Weeks");
	  addOpt(oCntrl,  1, "3 Weeks", "3 Weeks");
      addOpt(oCntrl,  2, "4 Weeks", "4 Weeks");
	  addOpt(oCntrl,  3, "5 Weeks", "5 Weeks");
      addOpt(oCntrl,  4, "6 Weeks", "6 Weeks");
	  addOpt(oCntrl,  5, "7 Weeks", "7 Weeks");
      addOpt(oCntrl,  6, "8 Weeks", "8 Weeks");
	  addOpt(oCntrl,  7, "Other", "Other");
      break;
     case 1: 
      addOpt(oCntrl,  0, "2 Weeks", "2 Weeks");
	  addOpt(oCntrl,  1, "3 Weeks", "3 Weeks");
      addOpt(oCntrl,  2, "4 Weeks", "4 Weeks");
	  addOpt(oCntrl,  3, "5 Weeks", "5 Weeks");
      addOpt(oCntrl,  4, "6 Weeks", "6 Weeks");
	  addOpt(oCntrl,  5, "7 Weeks", "7 Weeks");
      addOpt(oCntrl,  6, "8 Weeks", "8 Weeks");
	  addOpt(oCntrl,  7, "Other", "Other");
      break;
     case 2: 
	  addOpt(oCntrl,  0, "1 Week", "1 Week");
      addOpt(oCntrl,  1, "2 Weeks", "2 Weeks");
	  addOpt(oCntrl,  2, "3 Weeks", "3 Weeks");
      addOpt(oCntrl,  3, "4 Weeks", "4 Weeks");
	  addOpt(oCntrl,  4, "5 Weeks", "5 Weeks");
      addOpt(oCntrl,  5, "6 Weeks", "6 Weeks");
	  addOpt(oCntrl,  6, "7 Weeks", "7 Weeks");
      addOpt(oCntrl,  7, "8 Weeks", "8 Weeks");
	  addOpt(oCntrl,  8, "Other", "Other");
      break;
    }
   }