[fizzle]

JS

var q = '4';
	function checkQ()
	{
	document.getElementById("sub").disabled = true;
	if(document.getElementById("q1").value == q)
	{
	document.getElementById("sub").disabled = false;
	document.getElementById("sub").style.border = '2px solid #00FF00';
	}
    }

И сам HTML

<table class=head cellSpacing=5 cellPadding=5 align=center order=0>
	<tbody>
	<tr class=rows>
	<td>2 + 2 =</td>
	<td><input id="q1" onkeyup="checkQ()"><td> 
	</tr>
	</tbody>
	</table>
	 
	<table class=head cellSpacing=5 cellPadding=5 align=center border=0>
	<tbody>
	<tr>
	<td>
	<form action="" method="" name="goNext">
	<input name="next" type="submit" value="Next" id="sub" disabled="disabled">
	</form>
	</td>
	</tr>
	</tbody>
	</table>