Update... got it working!
OK, turns out I have a LIDE 30 instead of a LIDE 50. Same difference; Canon refuses to support it on 10.6.
Here's what I've gathered from my research. The SANE package allows all sorts of previously-incompatible scanners to be used. Install the back-end, good deal. However (and here's where my understanding is still a bit shaky) the Image Capture app doesn't actually talk directly to SANE. Image Capture needs a TWAIN source, which is why you need to install the TWAIN-SANE bridge software.
However, the TWAIN-SANE package is apparently quite unstable. This could explain why my LIDE scanner was dropping on and off with Image Capture. Photoshop also acted up when I tried to import from the LIDE (again, through the TWAIN package, which makes it available to all TWAIN-capable apps).
The result is that we need some kind of software that talks directly to SANE, without the unstable TWAIN converter. You can do this through the command line using the "scanimage" command, which is sort of kludgy and probably not acceptable for your students. There is, however, an app called Snac which talks directly to SANE. It's been working GREAT for me, and has a nice simple interface! ;D Get it here:
Snac - Mac OSX GUI for SANE scanimage
One caveat, however; I noticed that Snac is set to do a greyscale or black-and-white scan by default. When I tried previewing or scanning in that mode, I got an error saying that the mode was not supported. Changed it to Color and all was well!
Snac only saves in TIFF, so you'll have to make sure people then convert them in Preview so your hard drives don't get filled up unnecessarily. If you're clever, you can also just make/find an Automator action / droplet that will convert them to JPEG when the TIFFs are dragged on to it.
There's also a command called
sane-find-scanner that you can use in Terminal to verify that SANE can actually see your scanner in the first place. Just plug in your scanner and type in the command; see if it detects it.
Hope this helps, and good luck. I can't stand it when good hardware is wasted due to lack of good drivers!