<script language = "javascript">
	function checkedPoC( _obj ){
		if( _obj.checked ){
			document.Form1.txtPoC.disabled = true;
		}else{
			document.Form1.txtPoC.disabled = false;
		}
	}
</script>
<form name = 'Form1'>
	Estado: <input type = 'checkbox' id = 'checkPoC' name = 'checkPoC' onClick='javascript:checkedPoC(this);'>
	<input type = 'text' id = 'txtPoC' name = 'txtPoC'>
</form>