There is only one file type that uses the .T08 extension:
TaxCut 2008 Tax Return
Tax return file created by TaxCut 2008, a program that allows users to create U.S. federal and state tax returns for the 2008 tax year; contains tax forms and their fields that have been filled in by the user; can be printed or e-filed using TaxCut 2008.
TaxCut files use the extension "TXX," where "XX" is the tax year being filed. For example, .T07 files are for the 2007 tax year.
NOTE: TaxCut was re-branded as "H&R Block At Home" for the 2009 tax year. Data from T08 files may still be imported into At Home 2009.
Updated: July 6, 2010