Before reinstalling, it would be far less painful to try applying or reapplying the 10.6.8 Combo Update which will bring bring a new 5.0.5, then run Security Update 2013-001, which should bring it to 5.1.8.
The Combo Update is not a reinstall, it will just replace missing or damaged files, from 10.6.0 through 10.6.8, including, in this case, the Safari 5.0.5.
You won't have the hassle of running Software Update a zillion times for other items.
Message was edited by: WZZZ
There is something wrong with his machine.
I suspect corruption, anti-malware and/or malware itself, thus the #8 Reinstall Just OS X method should solve all those issues at once and then Software Update should work perfectly after that.
The new anti-malware Apple installed should flag and remove if any of it remains.
It wouldn't hurt if there isn't a problem neither.
magwire - as QuickTimeKirk suggests, you could be using an outdated Safari that isn't in Applications...
Open Safari from Applications & see what version is actually there.
You might already have 5.1.8, in which case the 'newer version' message on installing 5.1.7 is entirely normal, and you just need to use 5.1.8 & ignore/delete earlier ones.
what 'anti-malware and/or malware itself' causes an outdated Safari ?