Advice for a programmer trying to get into trading

I'm a computer programmer who will be starting at a BB bank in the fall. My job will be to work on projects for the firm's traders (IE: pricing algorithms). However, I would much rather be working as a trader.

It's my understanding that traders and desk managers are often willing to hire people with CS and Engineering backgrounds. What, exactly, would they be looking for in a CS major? What would they be concerned about?

How do I train myself so that these concerns aren't an issue?

I think that one of my big issues may be aggressiveness. I'm a relatively easy-going guy, which may be bad news if I want to be a trader. (That said, I'm extremely aggressive for a CS major; even an Engineer.) Has anyone else been in the same situation? How have you worked on being more aggressive and more decisive? How did you overcome the whole feeling of "Do I need to be aggressive with this guy, or should I just try and be nice?"

Thanks for all your help on any of these questions.

-MidwesternBumpkin