If you ever need to run Ruby Webrick or Mongrel other than the default port 3000 for Redmine or any other RoR app, you can do easily by running the command using the -p option like this:
[root@pm redmine-1.0.2]# ruby script/server -p 80 webrick -e production -d
Hopefully you, will see followign result:
=> Booting Mongrel
=> Rails 2.3.5 application starting on http://0.0.0.0:80
Cheers!