2006 Hyundai Tiburon Water in gas tank?

I just got a 2006 hyundai tiburon august 2009. Yesterday (2-12-10) my car started sputtering and whenever I stopped my car would try to move forward a little. Almost jumping. Like the engine was missing and picking back up. This morning I went to start my car and it wouldn't hardly start then when it did, my rpm's went up to like 7-8. Then it sounded like it kept trying to quit on me. So I gave it a little gas to try and atleast back it out of the driveway so I could get my mother's car out. It didn't move hardly at all. It felt as if it coasted back. Could I have water in my gas tank? Can I fix this myself? How much would it cost to take it to a hyundai dealership to get it fixed?