Carrie, just go to your local rink, strap some skates on and go for it! We have a couple of girls training with us who are larger, and they are getting a lot out of it in terms of exercise that's FUN!
And thank you D2BS, I kickstarted my weightloss with the Cambridge diet, but after a couple of weeks (and with the breakdown of my relationship with my ex-partner) I came off it and went solo. I discovered that having a few weeks on such a strict diet was enough to make me realise just how much I had been eating before, and what was now a "sensible" amount to eat. It's taken me a long time this way (four years from CD to now) but there's been no yo-yoing, no binge/diet cycle, just an understanding that I had to change my mindset towards food! I wish you the best of luck on your journey, if you can change your attitude to food you WILL do it!