Either that, or (not recommended really) you can enable the catch all route in routes.rb by uncommenting the line towards the bottom that looks like:
but read the line above that, which tells you that if you do that, you'll enable access to all actions in all controllers; probably not what you want to do.
My routes.rb has resources :rusers.
Try putting the following line into routes.rb:
map.connect 'user/logout', :controller => 'user', :action => 'logout'
This would be correct if you were on rails 2, but according to your earlier post, you said you've got resources :rusers, which would only work in rails3, I think. So, to add the custom route, do this:
match '/rusers/logout' :to=>'rusers#logout'
Go here and do some reading:
That should give you plenty to chew on and at least make the simple routing stuff clear.
Hope that helps you.