Multiple $_REQUEST vars=SQL Error?

[Fargo]

Why does the followin code produce a SQL error if there is more than one request variable defined in the url?

PHP Code:

if (empty($_REQUEST['siteid']))
{
$getgames = $DB_site->query("SELECT * FROM site_game_info");
}
else
{
$tempval = $_REQUEST['siteid'];
$getgames = $DB_site->query("SELECT * FROM site_game_info WHERE siteid=$tempval");
}
while($game = $DB_site->fetch_array($getgames))
{
//call bbcodeparse.php to parse bbcode within overview and requirements fields
require_once('./includes/functions_bbcodeparse.php');
$game['overview'] = parse_bbcode2($game['overview'], 1, 1, 1, 1);
$game['rec_sys_req'] = parse_bbcode2($game['rec_sys_req'], 1, 1, 1, 1);
$game['min_sys_req'] = parse_bbcode2($game['min_sys_req'], 1, 1, 1, 1);
eval('$games .= "' . fetch_template('gamedetail') . '";');
} 


as you can see, one of the request variables is siteid, however, most of the time there will be more than one variable defined. For example, a link to some specific content may look like this:

index.php?siteid=3?do=overview

The code above functions properly when ONLY siteid is being sent, but once do=overview has been added, I get a SQL error because $tempval is being filled not only with the value of siteid, but "?do=overview" as well.

What im trying to do is have the page first look at the siteid so it knows which set of records to pull from the table (currently, I have it coded where an empty $_REQUEST['siteid'] returns all records), then finally look at DO so it knows what action to perform/template to eval.

Can someone please point me in the right direction?