Hello Gitte,
To use the odd and even -attribute you have to be inside an
iteration.
<dtml-in someSequence>
<dtml-if sequence-id-odd>
<tr bgcolor="blue">
<dtml-else>
<tr bgcolor="red">
</dtml-if>
<td> some stuff here</td>
</tr>
</dtml-in>
Hope this helps.
Sven