You will need to use the meta_query variable like so:
$start = time(); //Now
$end= strtotime('+1 month'); //1 month ahead
query_posts(
'post_type' => 'event',
'post_status' => 'publish',
'posts_per_page' => '10',
'meta_query' => array(
array('key' => $prefix.'event_start_timestamp', 'value' => $start, 'compare' => '>=', 'type' => 'NUMERIC'),
array('key' => $prefix.'event_end_timestamp', 'value' => $end, 'compare' => '<=', 'type' => 'NUMERIC')
)
);