Does XP see the scanner from the control panel - system- devices? Even if it isn't sipported it should show up on the bus.
And check your BIOS settings to see if there are USB settings that might be affecting things.

Try booting knoppix with some cheatcodes noapci etc. see if something's getting in the way.

If your version supports it try booting with the 2.4 kernel, at he boot prompt type knoppix24...

Finally, take the thing to a different pc and see if it works.