Setup for Taxonomy throwing 404 constantly
Unexpected non-reachable pages you know that exist are 99% of the time a problem in the server-config.

mod_rewrite for apache needs to be enabled and you need to make sure AllowOverride All is enabled in your virtual host for your drupaldirectory. more here: http://drupal.org/node/54832

After you have this setup right you can also enable clean-urls and lose the ?q= in your url. Set it up @ admin/config/search/clean-urls.