Can anyone tell me when I have to start reporting my winnings..?

[benneh]

..or direct me to a post that ahs already discussed this.

I'm a lowly college student, and right now poker is my only income, and i've been making quite a bit, though I don't think i've withdrawn enough to be taxed on it (or taxed a significant amount at least). I never gave it a thought because I was simply playing for fun and withdrawing a few hundred when I needed to, but now i'm withdrawing a few grand every now and then, and i'm going to go car shopping soon, so a bit more is coming out this weekend. Can anyone help me out with how I can do this? Also, if I deposited 10 grand and won 20 grand, would I be taxed on 20 grand, or just my net gain of 10?

Thanks.