Weird htaccess/mod_rewrite problem

I’m running WP 1.0.1 Miles and I wanted to switch to nice URI’s using the .htaccess/mod_rewrite option.
So I set everything up in the admin-section and copied the code into my .htaccess file, in the root of my WP directory, BUT after I did that, I get a 403 Forbidden You don’t have permission to access / on this server message on whatever page I try to view. Mod_rewrite is enabled on my host’s server.
My .htaccess contents:
# this will make register globals off in wp's directory
# just put a '#' sign before these three lines if you don't want that
<IfModule mod_php4.c>
php_flag register_globals off
</IfModule>
# this will set the error_reporting level to remove 'Notices'
<IfModule mod_php4.c>
php_value error_reporting 247
</IfModule>
# This activates content negotiation, so instead of /archives.php you could just call
# a file as /archives . Same for any other file on your site. Try it out!
Options +Multiviews
RewriteEngine On
RewriteBase /
RewriteRule ^archives/([0-9]{4})?/?([0-9]{1,2})?/?([0-9]{1,2})?/?([0-9a-z-]+)?/?([0-9]+)?/?$ /index.php?year=$1&monthnum=$2&day=$3&name=$4&page=$5 [QSA]
RewriteRule ^archives/category/?(.*) /index.php?category_name=$1 [QSA]
Any ideas?