In addition to ArPaNET's advice - what will your employment status be? If you're going to be self-employed, you'll need to at least go to your county seat and establish a sole proprietorship (you won't even be allowed to open a business account without those documents, unless laws seriously differ across the US). You might be able to get away with a 1099-C (miscellaneous income considered as "non-employee income" on your personal tax return), but that's going to depend on the company you're working for. Forget about just pocketing the money, unless the company you're going to work for charges its customers under the table (never know with law firms) - the company you're working for will report the payments to the IRS, and you better make sure you report them, too.
Establishing a sole proprietorship in my county costs $9.95 - not too hefty a fine to make sure you're legal, I would think... Next you'll need to consider state and federal taxes, which will depend on your state - you might also be responsible for municipal taxes. Next up is insurance - you need to take into account that as a sole proprietor, you are personally responsible for any and all debt your proprietorship incurs, and that if you want health insurance... let's just not go there.
Not trying to scare anyone away from doing it - I actually think that it's one of those things everybody should at one point in their lives at least try. What I am trying to say is that if you're going to do it, do it the right way. I've got a pretty solid customer base (I started with less than $200, and never used any personal capital other than that initial investment), but I'm not making nearly as much as I would make working for an employer - that's not really a problem right now (I'm still going to college more-than-full-time, and insurance and other stuff are being taken care of by the wife), but it would be tough to make this into a "real" job (I would have to work more than I'm willing to to make a decent living).
Feel free to send me a PM - I believe I've got a bunch of mistakes I have learned from doing this "self-employment" thing ;)
