I went through the sources (http://easynews.dl.sourceforge.net/sourceforge/hp3300backend/backend-20060304.tar.gz
). The INSTALL file is very informative. Read the file and build the testtool as instructed (just run make). Then run ./testtool and see what happens. It just told me I didn't have the scanner. lol I did run ./testtool -h and it does have some interesting options. Don't know if the driver has to be installed first or not for it to do those neat things with your scanner.
To actually install the driver will be a pain. You need to uninstall Sane. Then patch the sources, build it and install.
Our Slackware Sane package doesn't make that easy for you as the frontend, and backend and some other doo-dads are all rolled up in one package.
If you can wait a day or two, I'll build you a custom sane package that shouldn't give you any dependency issues with other packages. Just PM with with a email, ftp, credit card and Social Security number and I'll get it to you.
Or just a email address that can handle a +- 1mb attachment.