[MBmusic]

ну сделал то что вы написали выше)

<script type="text/javascript">
  function showOrHide(cat1, cat2) {
    cat1 = document.getElementById(cat1);
    cat2 = document.getElementById(cat2);

    cat1.style.display = "block";
    cat2.style.display = "none";
  }
</script>

<tr>
            <td width="100">Користувач</td>
            <td><input type = "radio" id = "cb1" onchange = "showOrHide('cb1', 'cat1');" name="student" value="0"></td>
			<td><input type = "radio" id = "cb2" onchange = "showOrHide('cb2', 'cat2');" name="student" value="1"></td>
            </tr>
			<tr id = 'cat1' style = 'display: none;'>
				<td>Первый</td>
			</tr>
			<tr id = 'cat2' style = 'display: none;'>
				<td>Второй</td>
			</tr>