If you are talking about income for tax year 2006, you certainly can still file a return for 2006. The tax year should appear on the W-2.
In general, if you owe taxes, the government has no deadline to come after you for the taxes if you never file a return for that year. If you get a refund, you lose your right to the refund after 3 years from the due date of that return. In general, the due date for an income tax return for a particular year is April 15 of the following year. There are exceptions.
Anyway, if you have not filed any return for the relevant year, you are still within the time frame. If you did file a return, you still have time to file an amendment.
You may also have to file returns for the state and local governments.
If you turn out to owe taxes from that late year, you may be charged penalties and interest.
Any tax professional (Enrolled Agent, CPA, or attorney) likely still has the software to file returns from 2 years ago. If you want to do the return yourself, the IRS has blank forms from prior years at its website: www.irs.gov .