How do I file taxes for 2005 and what form should I be looking for?

Answer 1

If you filed the 2005 and forgot to include this income, you need to complete form 1040X http://www.irs.gov/pub/irs-pdf/f1040x.pdf

If you didn't file for 2005 and you have just the one W2 to file you can use the 1040EZ
http://www.irs.gov/pub/irs-prior/f1040ez--2005.pdf
Instructions for the 1040EZ
http://www.irs.gov/pub/irs-prior/i1040ez--2005.pdf

Answer 2

Did you file last year? If not then you will need to use one of the 1040 forms. If you already filed and need to make a correction, you will need to file a 1040X. Go to the IRS website and download the forms under the link "Forms and Publications" and mail it in.