Hi,
Here is the sample code how to fetch querystring and check in select tag. Just pass the querystring like.

http://yourdomain.com/yourpage.php?selCategory=2

<select name="selCategory">
<?php for($intI=1;$intI<=5;$intI++) { ?>
<option <?php if($intI==$_REQUEST["selCategory"]) { ?>selected<? } ?> value="<?=$intI?>"><?=$intI?></option>
<?php } ?>
</select>