You need to work on flexibility. I'd suggest doing some pilates, either in class, or getting some tapes. Perhaps there are some tapes that are solely leg stretches. Also, try raising one leg on a high surface (a ballet bar would be best, but I use my kitchen counter!) Keep trying to stretch your chest to your upper thigh.
The key is stretching more than anything. As for going from standing to a split, you need to work on sliding one leg back -- gradually at first, and your front leg will start to slide a bit forward. Try it with socks on a wood floor, if you can. It's a little easier than with bare feet. I have an easier time moving my right leg back, but I know some people are flexible enough to do either side.
Also, I've seen gymnasts who have some sort of raised matt and they put the front leg on that and the back leg on the floor. They just sit in that position for minutes on end.
Just be careful; you can really hurt yourself if you try to go too far and you don't yet have the flexibility to do so. And in dance, the splits are usually over and done with quick, so I wouldn't necessarily worry about getting all the way down.
Good luck!
