SlavaP, без id - только oninput="go(this);" data-pas="123" сделать и не менять положение кнопки далее
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="ru" xml:lang="ru">
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<title></title>
<script type="text/javascript">
function go(obj) {
var pas = obj.getAttribute("data-pas"), next = obj.nextElementSibling ;
if (obj.value == pas) {
next.removeAttribute('disabled')
} else {
next.setAttribute('disabled', 'disabled')
};
};
</script>
</HEAD>
<body>
<!-- **************************************** -->
<table border="0" cellpadding="0" cellspacing="0" align="center">
<tr>
<td>
<input type="text" size="10" value="" placeholder=" введи 123" oninput="go(this);" data-pas="123">
<input type="submit" value="Далее" disabled="disabled" >
</td>
</tr>
</table>
<!-- **************************************** -->
<table border="0" cellpadding="0" cellspacing="0" align="center">
<tr>
<td>
<input type="text" size="10" value="" placeholder=" введи 123" oninput="go(this);" data-pas="123">
<input type="submit" value="Далее" disabled="disabled" >
</td>
</tr>
</table>
<!-- **************************************** -->
</body>
</html>