If you're using the rss2html php-script which can be downloaded from www[dot]feedforall[dot]com/more-php.htm then you can add something like that in this script:
PHP Code:
$myfeeds[]='url_of_the_feed_1';
$myfeeds[]='url_of_the_feed_2';
$myfeeds[]='url_of_the_feed_3';
$myfeeds[]='url_of_the_feed_4';
$myfeeds[]='url_of_the_feed_5';
$myfeeds[]='url_of_the_feed_6';
$myfeeds[]='url_of_the_feed_7';
$myfeeds[]='url_of_the_feed_8';
$myfeeds[]='url_of_the_feed_9';
$myfeeds[]='url_of_the_feed_10';
$XMLfilename = rand(0,sizeof($myfeeds)-1);
Add this in the script where there is the line "$XMLfilename = "sample.xml";" by default.