That is indeed the best solution because your scanner can work directly from the original material, and Photoshop is limited to what was scanned.
In case the moir? patterns are difficult to remove, and this is often the case, you can always try changing the angle (I mean: align the photo the scannerwindow's edge, and then turn it slightly.) For a greyscale (black and white) image, try 15?, for a dark coloured one 15, and a lighter one 45?.
A second thing you can do when scanning screened images is scan at a very high resolution. ( at least 600spi (samples per inch))
A third thing is to always scan in RGB mode (colour mode) because it does give you more options.
I just remembered that I once found a Photoshop action somewhere on the net that should be useable as a descreen filter. I add it here.
Hope this helps as this is a tough problem, most certainly because it needs a sound basic knowledge of PS.
To know how to use an action, check out
this thread
In case you run into difficulties, just say so and we will see what we can do.
(May I suggest to read the help files in Photoshop? If you're so lucky as to have Acrobat (not Acrobat Reader) or know someone who does: Acrobat has an option to turn the complete set of html pages into a pdf which is printable) The Help files are a hidden treasure, and in fact a very readable and thorough free book on PS.)