well, Im not going to show you how to password protect feeds, and I dont even agree with what you are doing - but I dont read your site, so I guess I dont care.
I will give you some code and let you run with it..
RewriteCond %{HTTP_USER_AGENT} FeedBurner
RewriteRule ^(.*)feed/(feed|rdf|rss|rss2|atom)/?$ /index.php?&feed=$1 [QSA,L]
RewriteCond %{HTTP_USER_AGENT} FeedBurner
RewriteRule ^(.*)(feed|rdf|rss|rss2|atom)/?$ /index.php?&feed=$1 [QSA,L]
RewriteCond %{HTTP_USER_AGENT} !FeedBurner
RewriteRule ^(.*)feed/?([_0-9a-z-]+)?/?$ http://feeds.feedburner.com/village-idiot [R,L]
The above, if placed before the rules that wordpress uses will redirect anyone and everyone that doesn't have the feedburner UA over to feedburner.
You can obviously adjust the rewrite condition:
RewriteCond %{HTTP_USER_AGENT} FeedBurner
to something else, check the referer maybe.. and if not coming from feedburner, send them to a hardcoded XML file that explains what you want them to do.
Good luck!