The easiest way to do it is something like:
add_tab do |t|
t.named "photos"
t.links_to :controller => 'photos', :action => 'index', :product_id => 1
end
otherwise you can use the hash_for_ version of your named route, something like:
add_tab do |t|
t.named "photos"
t.links_to hash_for_product_photos(@product)
end
the exact syntax depends on which rails version you're using and how you configured your resources (prefixes and so on..)
Paolo