Again, another "not so interesting for blog stuff" type post. If you're displaying several rows of data and would like to alternate the background colors of the rows so they're easier to read:
<? for ($i=0; $i<$someNumber; $i++) { ?>
<tr <? if ($i%2) { ?> bgcolor="#CCCCCC" <? } ?>>
<td>data</td>
<td>more data</td>
</tr>
<? } ?>
that "$i%2" basically checks to see if $i is even or not, and if it is, print that "bgcolor" thingy so that it will color the background of that row.