If the scanner is a major brand unit, then you should be able to download drivers from the manufacurers site. Apple does include some generic drivers for usb devices, but I don't know how well they would work with a scanner. Plug it into you Mac, if the drivers aren't there already you should get a dialog box asking if you want to look on the internet for drivers. Other than that I'll have to leave to other posters here it answer your question.
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"life is pain, Highness, anyone who tells you different is selling something."--The Man in Black from The Princess Bride