This javascript cut & paste code snippet limits the number of check boxes that the user may select on your page. This script is ideal for situations where more than one selection may be allowed up to a certain limited number. If the viewer selects more than the allowed amount, they are notified of the maximum allowed and their last entry becomes invalid and unchecked. 

Insert this code into your HEAD of HTML

<!-- // == This Script Free To Use Providing This Notice Remains == // // == This Script Has Been Found In The http://www.DesignerWiz.com Javascript Public Archive Library == // // == NOTICE: Though This Material May Have Been In A Public Depository, Certain Author Copyright Restrictions May Apply == // --><script language="JavaScript" type="text/javascript"> <!-- Original: Glenn Wang (brief@ix.netcom.com) --> <!-- Web Site: http://capsule.bayside.net/ --> <!-- Modified by Ronnie T. Moore (The JavaScript Source) --> <!-- This script and many more are available free online at --> <!-- The JavaScript Source!! http://javascript.internet.com --> <!-- Begin function countChoices(obj) { max = 2; // max. number allowed at a time box1 = obj.form.box1.checked; // your checkboxes here box2 = obj.form.box2.checked; box3 = obj.form.box3.checked; // add more if necessary count = (box1 ? 1 : 0) + (box2 ? 1 : 0) + (box3 ? 1 : 0); // If you have more checkboxes on your form // add more (box_ ? 1 : 0) 's separated by '+' if (count > max) { alert("Oops! You can only choose up to " + max + " choices! \nUncheck an option if you want to pick another."); obj.checked = false; } } // End --> </script>

Insert this code into your BODY section

<center> <form> Please choose up to 2 sections: <p><input type=checkbox name=box1 onClick="countChoices(this)">Section 1 <p><input type=checkbox name=box2 onClick="countChoices(this)">Section 2 <p><input type=checkbox name=box3 onClick="countChoices(this)">Section 3 <p></form></center>

Simply Cut and Paste Script code
Be sure to properly place script position in HEAD & BODY sections of html 

This script has been in the Internet.com Public Library.