Sounds like you've already have an advantage being a distance runner. It's great that your looking to cross train with triathlons. Looking into swimming early will definately give you an edge. It's a part of the sport that is usually overlooked by many triathletes. Lessons would be great just to get some good swimming form down Another idea would be to to find a local triathlon group in your area and train with them on their swims (openwater/pool). Definately would help to get some tips from people who are already doing what your looking to do.

Hope this helps. Good luck with your swimming.