Re: feeling underpaid
Often the best way to have the salary discussion it to start a discussion with your supervisor about your performance. If you get good feedback during that discussion, then try and figure out what you are worth to your company (not what you think your worth is).
So, determine what your value is to your company. Quantify it and come up with some data (proof). And then go into the salary chat with your boss. If they value you and you can show you are undervalued, then you might do OK.
On the other side of the coin, however, the fastest way to end a raise discussion is to go in and talk about how you are underpaid and how you can get more somewhere else. If you do that, chances are your boss will call your bluff and tell you to see if you can do better elsewhere.