The only way to open a .tax file from 2004 is with the TurboTax software for 2004. The software is no longer available. If you don't have a working copy, you could try TaxPrinter. You send them your .tax file and they send you back a PDF of the tax return, which you can then print with Acrobat Reader.
TaxPrinter has no connection with TurboTax. I have never used TaxPrinter, so I cannot make a recommendation. I'm just making you aware of it.
