YAY runners! I love when people get excited about running! I agree that good running shoes are a MUST. I would avoid the sports stores, however, and go to a running store if at all possible. The staff there should be trained in how to evaluate your gait (how you walk), the wear on your current shoes which demonstrates where you apply more pressure on your shoe, how wide your foot is, how high your arch is, etc... When I 1st started running I was in the absolute wrong shoe for my foot type, and since my change I've been a happy girl:)
I'd suggest buying some books on running also. Hal Higdon is a running guru who has some good book out. Before my 1st marathon, I bought and read The Non-Runners Marathon Trainer Amazon.com: The Non-Runner's Marathon Trainer (9781570281822): David Whitsett, Forrest Dolgener, Tanjala Kole: Books. Awesome book for inspiration and to get you ready to finish your 1st marathon.
I also was never a runner until medical school. I used to do tons of cardio weekly, but never ran, and when I 1st started running I couldn't even go 5 minutes without stopping! I now run several half marathons a year, and have completed 5 full marathons. The feeling of crossing any finish line during a race is worth all of the training:)
Good luck and great goal to set! Once you get started you'll be hooked!