Checkbox-- Select at least one box using jQuery

Code:

<script>
$(document).ready(function () {
$('.error').hide();
$('.submit').click(function (event) {
var count = $('input:checked').length;
if (count == 0) {
alert("select at least one");
return false;
}
else
{
return true;
}
});
});
</script>

<input id="app" class="box" value="5" type="checkbox" name="apple">Apple$5

<input id="ora" class="box" value="2" type="checkbox" name="orange">Orange $2

<input id="mel" class="box" value="1" type="checkbox" name="melon">Melon$1

<input id="gra" class="box" value="3" type="checkbox" name="grape">Grapes $3

<input class="submit" value="Submit" type="submit">

more:
http://code.google.com/p/m-jq-projects/wiki/enableControlOnCheck_jQuery