This is tested on Internet Explorer only. Note, that it seems mandatory to append the child to the tBody collection of a table (at least in IE).
<html>
<head>
<script language='javascript'>
function addRow(a,b) {
var r = document.createElement('tr');
var ca = document.createElement('td');
var cb = document.createElement('td');
var ta = document.createTextNode(a);
var tb = document.createTextNode(b);
var t = document.getElementById('tbl');
ca.appendChild(ta);
cb.appendChild(tb);
r.appendChild(ca);
r.appendChild(cb);
t.tBodies(0).appendChild(r);
}
</script>
</head>
<body>
<form>
Column A: <input type=text name=a>
<br>Column B: <input type=text name=b>
<br><input type=button value='add Row' onClick='javascript:addRow(a.value, b.value)'>
</form>
<table id=tbl>
<tr><td>Column A</td><td>Column B</td></tr>
</table>
</body>
</html>