I've got a long running cgi script that I use to keep track of some statistics.  It just sits in the background and checks the database periodically.  This script worked fine under the most recent version of php3:

#!/usr/local/bin/php -q
<script language=php>
set_time_limit( 0 );

// set up variables

while( true ) {
    mysql_connect( $server, $user, $password );
    mysql_select_db( $dbName );
    $results = mysql_query( $query );
    $row = mysql_fetch_array( $results );
	
    // do some stuff

    mysql_free_result( $results );
    mysql_close();

    sleep( 15*60 );
}
</script>

Email me if you need any more information.