Click Check Box to Enable Form Input
HTML
<form name="form1">
<div class="controlset-pad">
<input type="checkbox" name="others" id="medium" />
</div>
<div class="field4">
<label>Click the check box to enable the input</label><br />
<input type="text" name="other_name" class="medium" disabled="disabled" />
</div>
</form>
JavaScript
$("#medium").click(function() {
$(".medium").attr("disabled", !this.checked);
});