This is from another forum as I was looking for the answer to the same issue:
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First off, when Samsung labels a button "Scan to PC", they mean it. That button only works with Windows PCs not Macs.
To get it to the Samsung SCX 4500 to scan on your Mac you need to acquire the image using some other software. I used Preview.
Put the picture or document that you want scanned on the bed. Open Preview. From the File menu, select the Import Image... option.
The scanner activates and you will see, you guessed it, a preview of what is to be scanned. Notice that the scan button is grayed out.
You now have to click and drag a box around what you want scanned. Once you draw your box identifying the exact image to be scanned, the Scan button is enabled. Now adjust any options, and hit Scan. Enjoy.
Thanks to the Apple Genius in Century City who helped me out, also this post was helpful:
http://discussions.apple.com/thread....sageID=5800155