What was the total amount of your earnings for 2007 (in box 1 of your W-2)? Is it a small sum (say a couple thousand dollars)?
If you made $3000, for example, you more than likely had no Federal taxes withheld from your paychecks. If you rec'd a relatively "low" amount in your total pay each week (for example $100) and/or you claimed multiple exemptions on your W-4, you probably wouldn't have any Federal withholding.
This shouldn't necessarily be a problem when you file your return (if the above scenario I suggested is accurate). It's possible you may not owe any taxes, so no withholding is ok. It just means you MAY not get a refund (assuming you don't have any dependents, which could result in you receiving a refund due to Earned Income Credit).
If your earnings for 2007 were a larger amount, say for example $25,000, no withholding could result in you owing the IRS.
If you are unsure if your W-2 is correct, take a look @ your FINAL pay-stub from 2007. If it doesn't show any YTD (Year to Date) Fed withholding, then your W-2 is most likely correct. If you didn't keep your pay-stubs, or your are STILL uncertain if your W-2 is accurate, ask your manager or someone in human resources (whoever handles your paychecks/payroll) to verify the totals on the W-2.
Bottom line - Just because you didn't have any Fed taxes withheld, that doesn't mean you will have any problems when you file your return.
If it turns out you actually owe the IRS (which I doubt if your situation matches the scenario I presented @ the start of this answer), you can wait until April 15th to file your return and write the IRS a check. In that case, I would suggest filling out a new W-4 form so you will have Federal taxes deducted/withheld from your paychecks this year.