This is a program that automatically adds nikkud to Hebrew text in any Windows word-processor. I haven't tried it though.
I do have Sapir for Dos with Auto-nikkud, but I doubt this software is available anyware legally any more. And it will only work under Dos-compatible OSes such as Win 9x or Dos.
The latest version of <A href="http://mplaut.tripod.com>Sapir for Windows</a> includes a wizard that converts from Sapir for Dos to Windows-compatible Hebrew text. I don't remember if I checked its capabilities of converting text with Nikkud, though.