Archives by month – custom template?

I finally got my archives page to work by creating a new “Page” in the admin area and assigning the archives.php template to it. This page works fine, but the links to my montly archives all lead to a 404 error page. The monthly archive links look like this:

http://mydomain.com/2010/12/

I have selected the “Month and name” option for my permalink structure. My .htaccess looks like this:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

The only plugin I have active is WassUp.

So here’s my question… is WordPress looking for a particular template page to go with it just like archives.php and about.php? And, if so, what would this page be named? I know that month.php doesn’t work (I tried in on a whim).

Any help or clues are highly appreciated – thanks!