basic question: linking with multiple parameters

My thinking is not really restful in this matter so I may be trying to
do this the wrong way.

I want to link to an action needing two parameters (two ids). One for
the currently selected folder and one for the currently selected file
in that folder.

<%= link_to file.filename, {:action => :show, :id =>
@selected_folder, :file_id => file} %>

I get:

I want:

I am still trying to figure out if I need to do something in routes.rb
or in the controller or when calling link_to... or a combination of

Any ideas of which direction to go instead for this kind of interface?
How to do it restful (resource mapped?)

Thanks in advance for any hints or ideas.


Typical, sorry for taking up space...
5 min after posting I stumbled onto something on google

For the record:
Any extra parameters need a route. So in my example that would be

map.connect 'files/show/:id/:file_id', :controller => 'files', :action
=> 'show'