You have to access the columns to calculate the right value:
$sitealerts = mysql_query("SELECT * FROM siteconfig WHERE setting='adminalerts'");
//if the query was OK
if($sitealerts) {
//loop through all result rows
while(FALSE !== ($row = mysql_fetch_assoc($sitealerts))) {
//do the calculation
$count = 0;
$count += intval($row['nauseralert']);
$count += intval($row['mmsitealert']);
if($count > 0) {
print $count;
}
print '<br />';
}
mysql_free_result($sitealerts);
}