Here's the best way I've found so far to convert slides and negatives to WWW-usable digital images:

• Get them digitized onto a Photo CD. To a Sun workstation Photo CDs look just like standard IBM-PC CDROMs. In a subdirectory ``images'' you'll find a bunch of ``.pcd'' files (``imgNNN.pcd''). Each contains one image at 5 resolutions, the highest being 2048x3072, which seems to capture about all the information there is on a slide for films ASA 200 and higher. The middle resolution is probably the one you'll mostly use for internet use.
• Convert the Photo-CD files to GIF or JPEG. The more expensive commercial packages will usually support Photo-CD format (although Corel-draw 5.0 crashed whenever I tried to get it to read my Photo-CD). If you're cheap and know Unix, then you can instead download and compile the package ``Imagemagick'', which is free. That's what I did. It also supports arbitrary rotations, which can be useful if you don't always hold the camera level.
• I found ``xv'' useful for cropping images interactively, but keep in mind it won't preserve more resolution than will fit on your screen. (It also won't preserve more than 256 colors.) For large or full-color images use xv to give you coordinates, and then use those coordinates as geometry options in Imagemagick to actually do the cropping.