Contrary to some opinions, antitrust is not necessarily anathema to the conservative position. Monopoly business practices are impediments to a free market economy.
On a more practical basis, the conservative camp also includes many bankers and other businessmen who are threatened by the MS monopoly. Old companies like Kodak lodging complaints are a much wider story than software companies like Sun, Novell or Netscape worrying about their competitive position. MS has made a lot of corporate enemies and has not won many friends in those businesses wishing to enter the internet economy.