The file-swapping software firm filed an opposition brief on July 3, highlighted by an antitrust defense against the RIAA’s injunction motion asking a federal district court to shut down Napster’s voluminous music directories.

The company is reaching for the heavy artillery to defend itself. Recently, Napster hired David Boies, the U.S. Justice Department’s lead attorney in the antitrust case that resulted in Microsoft being split in two.

Boies isn’t content to rest his case on antitrust issues: he’s offered three other lines of defense as well.

A second argument cited a 1984 Supreme Court decision in the so-called “Betamax case.” The decision held that as long as a technology is “capable of substantial non-infringing uses,” making a technology available doesn’t infringe on copyrights, even where it may encourage or be used for infringing activity.

That argument helped derail efforts to banish the VCR in the 1980s. Napster points out that its software provides a “music community” where members may chat and swap information, and lesser-known artists may promote their own music by sharing their MP3 files.

The service allows established artists to make concert tracks available for promotion purposes and supports copyright-friendly Windows Media Audio files. Another service is “space shifting,” the practice of letting consumers access their own recordings from a number of different computers.

As a third defense, Boies cited the Audio Home Recording Act, also referred to as the “Diamond decision,” that protects the right to manufacture MP3 players. Under the AHRA, “consumers have an absolute right to create and transfer digital music for noncommercial purposes,” according to the brief.

The RIAA has argued that Napster users infringe on copyright protections by sharing files for personal use.

Boies’ fourth defense argued that Napster users are protected under fair-use clauses. The RIAA has countered that the service is being used for commercial purposes.

U.S. District Judge Marilyn Hall Patel will review the arguments and is expected to rule July 26 on the RIAA’s motion for injunction.