Lucky you! I can't imagine finding them in the trash! Even if you didn't know how to use them, they're gorgeous pieces of machinery. I can't imagine tossing something so intricately made.
The 890 shouldn't be too different from the 860. If you can get to the Brother FTP site where they have the manuals, I think there's a 891 manual there that should be very close to the 890. If not, the basics for casting on and such are probably the same for the 860 and 890.
Have fun! If you're on Ravelry, there are a lot more machine knitters over there (at least three groups), so someone's bound to be able to help with any questions.