This cheap version imports encore, rhapsody, midiscan and smartscore. It converts internally from uncompressed TIF format, the module being a basic one but useful in that you need not pay for another program unless converting lots of scans and want to save time.
I use smartscore and that's the best I've found so far.
It's a few years since I used midiscan, the files were saved as mnod (.mnd), and finale can import these but I see no specific input for the general niff format, and have no files to try anymore. I remember I used to have a mnod to niff converter... maybe there's another around to go in the opposite direction?
I forgot to mention Noteworthy Composer, this is about half the price of Finale Print Music and also very good though not as flexible. They also list XP as an option.
Try loading the software in 95 or 98 compatabilty mode.