I also have used .mod_rewrite for the URL to remove the .php.
While testing my site, I noticed that a '/' after the page name prevents the menu from working.
RewriteRule ^photo-series$ /photo-series.php
RewriteRule ^photo-series/ /photo-series.php/$1
Does not work: http://test.twincitiesrailfan.com/photo-series/?id=1 (mouse over 'photos' or 'text' in the menu bar.)
Does work: http://test.twincitiesrailfan.com/photo-series?id=1
While the URL is not as neat as I would wish, it works and I don't have to do alot of scripting. I am wondering what the problem is?