Yet another instructor weighing in. Previous posters are correct in stating that a class would do you the most good - nothing better than in person help as the instructor can actually see what you're doing and how your dog is responding and you have the built-in distractions of other people and dogs.
That said, Don Sullivan is a perfectly acceptable balanced trainer along the lines of William Koehler or Margot Woods and you should be able to see results. I have issues with trainers touting the leatest and greatest (the plastic "command collar" that comes with the system isn't necessary) but I realize that they need something to stand out from others. Dog training isn't magic - you don't need DVD's and fancy stuff - just a training collar, 6 ft lead, perhaps a longe line (Sullivan calls them "Freedom Lines") and a whole bunch of time, patience and consistency. In fact, if you want to spend less $$, pick up a copy of The Koehler method of Dog Training on eBay. Follow it step by step and ignore the last chapter, which deals with problem dogs. If you have a problem dog, you need in-person help.