How do I obtain my 2007 tax return when I lost it!

You can get copy of tax return on payment or transcripts of tax return for free from the IRS. Transcripts have all the information.
Read Copy of tax return and transcripts, Your U.S. Tax Return: The U.S. Income Tax Topics 1 (http://taxipay.blogspot.com/2008/08/us-income-tax-topics-1.html)

If you live near a IRS office, you can merely go in and get a copy for free

Also, if you had the return done professionally, the tax pro has a file copy. Expect to pay a small $5 to $10 handling fee to get another copy of the return.