I'm also just getting started with step. I've found two beginner videos that seem really neat. The first is Gin Miller's Everybody Steps. It's by the girl that "invented" step aerobics!
The second video I order is Debra Mazda's Let's Get Stepping. Debra used to be over 300lbs and is now a size 12. The girls in her videos are bigger, so I feel comfortable with that.
I haven't tried these yet, as I just ordered them yesterday, but I've done some research for the last couple weeks and decided on those. There's video clips of these at collagevideo. I hope that helps you a little.