Would recommend escaping the full stop:
RewriteRule ^(index|atom[0-9]*|rss|b2rss|b2rdf)\.(rss|rdf|rss2|xml)$ rss.php?file=$1&ext=$2
Would recommend escaping the full stop:
RewriteRule ^(index|atom[0-9]*|rss|b2rss|b2rdf)\.(rss|rdf|rss2|xml)$ rss.php?file=$1&ext=$2