Cleaning Raw Scans
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 software. This guide will teach you how to deal with typical half-tone type screening noise.
Download the free image manipulating software, Paint.net from here: http://www.getpaint.net/ Although version 4.0 still in beta stage, for performance reasons, I recommend to use of this version because its redrawing/rotating/loading speed is much faster than the stable version.
If you encountered any bugs, uninstall it and use version 3.5.11.
Next, open the raw scan you acquired from the scanner. Saving the image to TIFF is preferred 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 obvious 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 while scanning the image, and the printing quality of the book.