 
well, i have lots of experience with scanning in images and altering
them.  as for changing them back into negatives, is that really possible?
scanning and altering is no big deal. i don't know what types of
features you have in your version of photoshop.  but the one i use
(which, incidentally is on a quadra) has gallery effects and all types
of other neato stuff.
i'm just wondering why you would want to put your images back into
negatives, because once you print the image out-that's your print.
do you know what exactly your aim is in all of this?  like, are you
doing this just for fun, for a business, to gain more computer
knowledge, for a project you're working on....
otherwise, i guess i don't know if i'd be helping or not by posting info
on scanning and stuff.
ok?  cool.
seeya