Unable to select twain source error message, how I hate thee.
If you're reading this, you either already know me and will be bored, or you're someone who is desperately searching for the same solutions I was searching for. You've probably already found the same forums and discussions I found, as well as the official Canon site where you can get some drivers and so forth. So this may not offer anything new (or good), except the understanding that I gained.
My husband (TheLimey) and I spent a cumulative 12 hours (6 each!) or so trying to find a way to get my beloved, beloved Canon Lide 35 scanner to work with our new laptop, which is running Vista (64-bit).
To get to the nub of the matter, it can't work. Canon has downloadable drivers that will work for my Lide 35 with 32-bit Vista. It has drivers that will work for 64-bit Vista with the Lides above 35. But no drivers that will work for the Lide 20 or 35 with 64-bit Vista. Dammit.
Even an emulator (virtual machine) won't work, because it's the hardware, not the software. Supposedly there is a guy out there who got the drivers for the Lide 60 to work with his 35, but I'm suspicious after all our research. (We certainly couldn't get that to fly.)
If only Canon would just write a new driver for use with 64-bit Vista, then everything would work fine! But they probably want me to buy something new instead. Forget it.
My husband initially said that he'd be willing to wipe everything and install the ol' XP, but he later reneged, citing its 32-bit-ness and how it will halve our resources (memory) to use it. Instead, we'll be installing XP on our old "backup" desktop and (hopefully) using that for the scanner base. We just have to get an old monitor somewheres.
Oh, and in case you're appending that path in your environment variables and are wondering--as I did--what's the difference between WINNT and Windows, WINNT is just an older-school variable for the same thing. Try both.