Can I get a copy of my 2006 tax returns online?

You can get a free online transcript
Tax Topics - Topic 156 Copy of Your Tax Return – How to Get One

To have one mailed you have to fill out the form 4506 and costs $39.00

Tax Topic 156 in brief:
Normally, for most of the requirements your purpose is served if you ask IRS for Transcripts instead of your tax return. You can order a transcript by calling 1-800-829-1040, or using Form 4506-T, Request for Transcript of Tax Return. There is no fee for a transcript. Transcripts have most of the information from your tax return including information from W2, 1099.

Use Form 4506 is Request for Copy of Tax Return. You will get copy of tax return filed by you along with all the attachments (like W2, 1099.. ). For each return the charges are $39 and IRS takes about 60 days to complete your request.