Scanner help: can not install any scanner : is it possible to repair "still image" , i.e. scanners, part of registry in Windows XP without new installation?

Hello,
I have bought the 2rd scanner and alltogether I tried the 3rd scanner to
install and to use with WINDOWS XP Home edition, but the scanner part of my
registry must be destroyed:

The CANON LIDE 50 Scanner at the USB bus was found, but when I call the
scanner driver , the scanner is not found (cable not connected, but it is
connected, and using another PC the same scammer functions well!) , and the
HP scanner driver at the parallel port can not even be installed correctly,
because the registry entries from the inf file of the HP scanner are not
found changed after setup in the registry.

I have tried what I can : checking the registry entries I know, looking into
Internet, but although "The Windows XP is said to be the best Windows for
working with digital photographs. " (from Internet), no scanner cab be
correctly installed and and used!

But I can not make a new installation, because of the multitude of the
installed programs and because I need the so installed programs for my job,
and I can not make a parallel installation because I have an OEM version
with only "product recovery CD" - no additional installing of Windows XP in
another partition is possible!

Has anybody similar problems with scanner using Windows XP??

Has anybody a tip or an advice how to repair the registry manually or by a
program available??

Thank you very much for help!

TAH