IIS 6 and Isapi Rewrite

I’m having some trouble with pretty permalinks using WordPress 3.0.1 on IIS 6. I have followed this article: https://www.helicontech.com/articles/wordpress.htm.
I have post, page, category and tag urls working beautifully, but my Archive urls are broken. This is happening identically on two different WordPress installations.

I can get to my archives by going to mydomain.com/index.php/year/monthnum, but mydomain.com/year/monthnum yeilds a 404.

How can I change my rule to make this work with Archives as well?

My .htaccess file contains:

RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(\d+)/[^/]+/?$ index.php?p=$1 [NC,L]

My Permalink structure is /%postname%/

Thanks for any help!

Jack