64bit, you're stuffed
No, the 32-bit twain driver works fine on 64-bit WIn 7 - it just needs a 32-bit application to drive it. I've got a CanoScan 8400F working OK under Win 7 64-bit, using the 32-bit driver.
ISTR I got the driver here:
CanoScan 8000F
I'm not sure if it supports all features, such as a negative or slide scanner, but I've not found anything mine can't do under Win 7.
SD