Where did you get it? Did you use the Desktop program for 2000? You need that installed to open a .tax file.
If you have a .tax or .tax20xx file you need that year's Desktop program installed to open it.
Turbo Tax doesn't have programs older than 3 years. You might be able to find one on Ebay or Amazon or somewhere but you wouldn't be able to update it or download the state program.
You could try the TaxPrinter service (not connected with Turbo Tax) to convert a .tax file to pdf at
http://www.taxprinter.com
OR get a copy from the IRS -
http://www.irs.gov/Individuals/Get-Transcript
