Hey I got my Primax 4800 Direct working properly.
I hope this might help you. This is what I did.
I got the plustek driver source and then there was this newbie tutorial in the site. The tutorial wanted me to compile the kernel, save the kernel configuration etc. But I didn't do all that.
I just installed the kernel source files from the RedHat9 CD. Then I extracted the Plustek driver source files to a temporary folder.
Then I ran the configure in the extracted folder (./configure).
Then make. Then make Install. Then make load.
By now the plustek driver will be loaded. To check you can use lsmod and you can see all the modules that are loaded.
You may now run sane and the scanner will work.
To check that your make was successfull, you should get a file called pt_drv.o in the extracted folder. Then when you run make install check /dev/ for pt_drv.o. Then you are sure that the driver was compiled and installed in the proper path.
You will also have to change the /etc/modules.conf file so that the driver is automatically loaded when linux starts. This is explained in man sane-plustek
For more information check this tutorial which I found usefull. I skipped the kernel configuration and the IEEE something described in this tutorial, but the driver worked.
tell me if you get your scanner working !!!