RewriteRule ^([^admin|compose|error|home|register])/?$ index.php?section=pages&username=$1 [QSA,NC]

I'm looking to match /username/ (and not /admin/, /compose/, /error/, etc.) and direct to index.php?section=pages&username=username

So username can be anything but those words. I don't know why I can't get it working... I'm obsiously not very good with regular expressions. Think I'll sit down and read that huge tutorial in the PHP manual one day soon...

Any help at all would be great,

Aaron