mod_rewrite exclusion

I’ve got webstats in a virtual directory forwarded from /stats/ on my site. So when mod_rewrite see’s the directory /stats/ doesn’t exist, it goes ahead and rewrites the URI for WordPress. I’ve been toying with it for over an hour so far and I can’t get it to work properly. Here’s what I’ve got in my htaccess:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} -d !stats
RewriteRule . /index.php [L]
</IfModule>

Looks to me as though it should work, and it [i]does[/i] when I go to /stats/, but when I try to look at the root or any other WordPress page, I get a 500 internal server error.

Any tips? I’ve made it work with any URI containing “stats” but it’s a word I’m not going to be able to avoid in topic names, so that ain’t gonna cut it. Thanks!