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1. Software update doesn't find anything
2. Download.com just links to the Apple site which says it comes in the software update
 
If you put your OS X installation dvd into your Mac, there should be a folder for optional installs. Double click that, click the Option Installs file, and after going through the whole accepting of the license agreement, under applications you should find Safari there. Check it and click continue to install it.
 
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