I'd be interested in this topic as well. I've done about 500 scans (boxes, manuals...), and the vast majority of them have the same problem: Moiré patterns.
Can't tell the printer model right now... My native software includes descreen option, but it drops the image quality from 600dpi to 300 or less... (600 is the maximum resolution allowed).
As a result, I found that in my case the best option is to scan it at 600dpi, and then do some little arranges in Photoshop: Blur and a free plugin called Fourier Transform works acceptable.
I do think that descreen applies by itself some sort of Blur combined with other filters, but if your printer is good enough, you should be able to obtain better scans than me (the printer is one of the most important factors here, I suppose!).
Dustin Hubbard from the site Gaming Alexandria has published tons of my scans, but there you can see no moiré patterns in them; he has some not free software that descreens pretty well, but unfortunately I don't know which one it is. If you do your research, you'll probably find out about it, but I'm sure that it will be kinda expensive
Can you tell us wich software are you using??
"Saludos" from Spain!
