I made $15K in 2010, and my federal taxes withheld was about $1K. Why does it say I owe $63?

I am a full time student, 23 years old, and work part time. I live with my mom, who pays for my school and fully pays the mortgage on our house. I made 15K in 2010, federal taxes witheld is 1K. I selected "Can be claimed as dependent" and "Full-time student" somewhere on the form, and when I go to finished it says I owe $63. Why is this? The only expensesI have are driving, food, school supplies, etc. but I am looking forward to some kind of refund because I'm broke and to see this, I just don't get it. When I unselect "can be claimed as dependent" the amount to be awarded changes to $360 (which still isn't that much to me) but I guess it's something? I don't understand this. I use the H&R Block program on my mom's computer, and I ask her for some guidance but she is kind of passive about it and just like whatever it says is what is right yadda yadda. I don't want to milk the system here or break the law but I just would like to understand why I am not getting a lot of the $1K that was witheld from me back? And what is it that is making it say that I owe $63? Thanks.