I believe the easiest way is to have a data attribute in your input, guiding the jQuery load action. Something like:
<input class="loadhtml" data-html="page1" type="radio" name="options" id="option1">
<input class="loadhtml" data-html="page2" type="radio" name="options" id="option2">
<input class="loadhtml" data-html="page3" type="radio" name="options" id="option2">
and then
<script>
$('input.loadhtml').on('change', function(){
var data = $(this).data('html');
$('#main-content').load(data + '.html');
});
</script>
edit
A fiddle, with the only difference i alert(data) passed instead of calling load