Fax4Word uses the fax program that comes with Windows 2000 and Windows XP.
However you do not need to disable the other Fax Software. You can install the default Windows Fax printer and then make sure that Fax4Word knows which Fax printer to use.
To do this:
Click Tools-Fax4Word-Setup Fax Printer and choose the Windows Fax printer instead of the other printer.