Cleaning up Raw scan
First and foremost, I'm not expert or anything, although I'm still learing how to clean up my scans, but i already know how to deal with the simple screening noise effectively with free softwares. This guide will teach you how to deal with typical half-tone type screenring noise.
First, download the free image manipulating software, Paint.net from here : http://www.getpaint.net/ Althought the version 4.0 still in beta stage, but for performance reason, i recommend to use the 4.0 version because it redraws/rotating/loading speed is much more faster than the stable version. But if you encountered any bugs, uninstall it and use back the 3.5.11 version.
Second, open the raw scan you acquired from the scanner. Saving the image to TIFF is preffered because TIFF offer lossless compression at the cost of bulky file size(still better than 24bit BMP which offer no compression at all) Unlike JPEG which compress the image by using destructive lossy compression, like discarding the details human eyes cannot see and reduced chroma resolution(YCbCr 4:2:0).
Here you can see the obivious half tone noise (click the image for original resolution).
The most effective way to remove the screen is resize the to 50% of the original resolution, but depends on how many dpi you set during scanning the image, and the printing quality of the book.