I just went through a simliar situation. I did my engineering degree and had a 2.4/4 GPA. I didn't really like engineering so I didn't care about my marks (I just wanted a job). After that I have gone back to school to get a second undergrad degree in applied math (with a bunch of mathematical finance and econ courses) and have a GPA of 3.83/4. In my SOP I basically told the truth; that I didn't like electrical enigineering and that is why my marks where low. I then put a little portion in about how having performed poorly before forced me to identify what I really wanted to do. And now I am doing well. But we will see how admissions go, I should start hearing in about a month. Oh, I am applying to mathematical finance masters programs. Perhaps I will test the PhD finance waters next year but we will see.
In my opinion don't draw to much attention to a low GPA in the past. Focus on your most recent acheivments.
Good luck