@guinnee, I think you need a 301 redirect for what you're trying to accomplish, not mod_rewrite.
...though, I could be wrong, I have an .htaccess issue myself.
Also, sorry if you feel I'm hijacking your thread, but since mine is a similar issue, it's probably best I post here rather than start another.
My problem is that I want to ignore anything longer than what I'm rewriting,rather than throwing a 404 error.
Should strip: but-this-throws-an-error/
This is what I have:
RewriteRule ^tema/$ topics.php [L]
RewriteRule ^topic/$ topics.php [L]
RewriteRule ^topic/(.*)/$ topic.php?tag=$1 [L]
RewriteRule ^tema/(.*)/$ topic.php?tag=$1&language=es [L]
I should also mention I plan to add a third param to the query string, "page="
so ultimately: example.com/topic/correct-value/1/ <--(last param numeric only) will be allowed, anything else striped and redirected to /correct-value/