The IRS sets the level for “Who Must File” each year. If you are under 65 years old, the following responses apply for the 2006 tax year, some of them may be adjusted (but only slightly) for 2007.
If self-employed, you must file if you make earned more than $400 annually.
If you are claimed by someone else as a dependent, you must file if you earned more than $5150 annually, or over $850 in interest or dividend income.
If you are single and claim yourself as a dependent, you must file of you earned more than $8450.
Other filing status will have higher limits.
The details are shown here, see the charts Pages 12 and 13, at:
If you are entitled to refunds of any kind, you will have to file to get them.
If you file a return you will definitely have to include your W-2 wages.
Welcome to the wonderful world of us other taxpayers!