Finding out how much you owe is not that simple.
First of all, there is the question of the number of exemptions you are able to claim. If you are being claimed as a dependent by someone else, then you lose your personal exemption which will be $3400 in 2007.
Secondly, your $8-9k in income you stated is too broad. Is it all earned income from wages or did you have passive sources of income such as Dividends and/or Interest?
Thirdly, there is the issue of how much you paid in withholdings. You only get a refund back if you paid more then your taxable income.
For your situation, assuming it's all W-2 Wages, I would do the following:
1) Get your recent pay stub. You will need the following information:
b) Federal Withholding
the two figures in #1. You do that by taking the amount, dividing it by pay periods you got paid for and then multiplying it by total number of pay periods you will be working the entire year.
For instance, if I made 10k over 10 months, I would take 10k/10 which equals $1k a pay period and them multiplying it by 12 (twelve months in the pay year) to get 12,000 projected income for the year.
3) Fill out a dummy tax return.
The 2007 1040's are out and the link is provided at the bottom. Since your tax situation seems simple, you probably just need to enter your wages which will be your AGI (Line 37) and continue onward. The general flow for your situation is as follows.
<Exemption> (if you can take it)