Now my scanner works, what I did:
copied from debian lenny libsane-mustek_pp.so.1 and libsane-mustek_pp.so.1.0.19 and placed in
usr/local/lib/sane/libsane-mustek_pp.so.1
usr/local/lib/sane/libsane-mustek_pp.so.1.0.19
also copied
usr/local/etc/sane.d/mustek_pp.conf
usr/local/etc/sane.d/dll.conf
In mustek_pp.conf uncommented the line for my scanner.
In dll.conf uncommented the line for mustek_pp.
from a terminal:
sudo ldconfig (don't know if this is necessary)
sudo xsane
Added the above 4 files in /opt./.filetool.lst