I recently upgraded my kernel from 2.4.27 to 2.6.8 and had to fix my scanner that had stopped working.
With 2.4 kernels you can use either "scanner.o" kernel module OR "libusb" to detect scanner. 2.6 kernels use only "libusb".
I suggest "libusb", because it is not dependent on kernel drivers. Install it, and hotplug also. Make sure that hotplug is set up to change scanner permissions to "root.scanner", "rwrw--" or similar. "Libsane" should take care of adding a hotplug script that does the permission changes.
After that, add users to "scanner" group, and after replugging the (usb) scanner everything should work. Check "man usermod" for info on adding users to groups. "Usermod -G" is the key.
I notice on my Debian that the scanner permissions are "root.root", "rw----" until I unplug and replug the scanner. So if the scanner is connected at boot time, it will work only as root.
Check "Scanner howto" for more information. I hope this helps you...