I earned $994 in 2006, and no federal income tax was taken out. Should I file?

If the income was reported to you on a W-2, and it was your only income, no - you are not required to file. If it was reported on a 1099-MISC, then yes, you have to file, using a Schedule C on the 1040.
There's no need to file unless you're eligible for the EITC. To be eligible you must have one or more qualifying children OR be between 25 and 64 if you have no qualifying children.
By filing you may receive a refund. Are you a dependent? Then no, there is no reason to file. Are you not a dependent? Then file your return. At least you will get the telephone excise tax credit. If you are between the ages of 25 and 64, and have no children living with you, you may get Earned Income Credit. If you have a child living with you, even if your child is not your dependent, then you may get a larger Earned Income Credit.
Try using Turbo Tax Online. There is no cost to use it unless you actually file. Fill out everything they ask you and if you'll get a refund then file, if not don't worry about it.
your not required to file however if you have children or qualify for EIC you may want to as this will be free money on top of the Telephone tax Credit which is $30 and then $10 for every other person on the return.