The comment form should be displayed on the same page as the article. It may not be obvious for people that they can comment, and even if they do, users are generally too lazy to comment if they have to as much as click once, whereas they may be more encouraged to do so if the form is there. it doesn't make sense from a usability point of view to be taken to a different page to comment. You may want to look at the way Slashdot handles the comments interface (or any other comment heavy website, like Huffington Post or Digg).
