[fastforward]

This may or may not help. It will probably confuse things even more

Here's what I have in my httpd.conf:

RewriteRule ^/f([0-9]+)/?$ /forumdisplay.php?forumid=$1&s=$2 [L]
RewriteRule ^/t([0-9]+)\.html$ /showthread.php?threadid=$1 [L]

I dispensed with the session tag as it wasn't really helping the spiders becaue the number would change each time anyway. I also edited all my templates to sort out the drop-down problems (I did this before I read porfiry's post).

In your problem examples I notice you don't start the url with a slash. You might want to try that. You never know.