I've found the best way to take care of moires right off the bat from film is to descreen, if possible, right with your scanner at the same linescreen as the media you're scanning (ie, if you're at 300dpi res, set descreen around 155lpi). That's removed most of the junk for me, but what heronheart says is true also, you do tend to get more moire in one channel than another, so that's something you'd definitely want to doublecheck even if you'd descreened right from the scan.