I think that you need to use other brackets like:

Page.all :conditions => ["parent_id is null and content_id <> '' and category_id = ?", params[:id]]

It's not safer, just some people prefer using the dynamic helpers.

Something else you should look at is named_scope. This let's you embed this sort of static condition in your model where it belongs.

I'm on my iphone so I can't test this (tested now) but you would add something like this to your model:

named_scope :top_dutch, :conditions => "parent_id is null and dutch_content <> ''"

I think you should then be able to do something like:

Page.top_dutch.find_all_by_page_category_id(4)

Check the API and test, sorry this is untested (tested now).

Edit: tested now, works as I suggested.

Happy to help, named_scope is an awesome feature for moving this sort of business logic back into the model.