Some all-in-one printers have negative scanning abilities. Are they standard size slides?
I have a ton from my grandfather and I haven't been too successful so far, but I have bee able to rig up my own ghetto style scanner.
I took my regular, old all-in-one Lexmark, removed the lid (it popped right out of its hinges, I think that is a feature) and then I built a frame from cardboard the same size as the glass on the printers scanner.
Then I stretched a plain opaque white trash bag over the frame and taped it all down. This created a "light box" type of apparatus. From there I put the negatives on the scanner glass, the frame over top of that and then I position a fluorescent light over the "light box" and scan as normal.
You must have some sort of back-light to get the scanner to read the negative correctly. Gimp can reverse the scan, and I think plain old "Paint" in windows can as well.
Here are a couple of the first ones I tried:
And, dear old Grandpa and Grandma:
