I ran a marathon at about your weight (I'm also 5'7"), properly trained of course. I started running when I broke through to under 200 lbs. This was 3+ years ago, and then again in the last year as I lost way too much pregnancy weight. Just remember to take care of yourself. While running itself doesn't cause arthritis, injury does, so be aware of overuse injuries, avoid them and take care of them early.
Good luck, and come join us on Cool Runners and let us know how it goes. I think there is also a C25K thread around here somewhere, that is named something incomprehensible for the uninitiated, so you may want to hunt around for it.
Long enough have you dream'd contemptible dreams,
Now I wash the gum from your eyes,
You must habit yourself to the dazzle of the light and of every moment of your life.
-from Song of Myself, Walt Whitman