click if/else problem

click if/else problem

Good afternoon.
I am new to javascript and brand new to jQuery.

I have little snippet I wrote to show or hide various <div>'s when a checkbox is clicked, depending on whether or not the checkbox is checked.

There are 5 categories of information being displayed in a table, and the idea is that the user can un-check a box to hide a category, and re-check the box to show the category. There is also a 'show all' checkbox that will show all of the div's.

The code I am using is as follows:
   $("#cal-all").click(function(){
      if($(this).attr("checked" == true)){
         $("#cal-all").attr("disabled", "disabled");
         $("#cal-head input:not(#cal-all)").attr("checked", "checked");
         $("table.calendar div").show();
      }
   });
   $("#cal-head input:not(#cal-all)").click(function(){
      var classMatch = $(this).attr("id");
      if($(this).attr("checked" == false)){
         $("div." + classMatch).hide();
         $("#cal-all").attr("checked", "");
         $("#cal-all").attr("disabled", "");
      }
      else{
         $("div." + classMatch).show();
      }
   });


Everything works as I want it to except for the last part - the 'else'.

When a box is unchecked, the corresponding div's are hidden.
When I click the 'show all' checkbox, all div's are shown.

But when I check a checkbox that had been un-checked, the corresponding div's are not shown.

Can anyone tell me what I may be doing wrong?
Any help greatly appreciated!