Sorry, this isn't true - 10.6.8 only works with Safari max. 5.1.8 which came some days ago with the Security Update 2013-001.
I had the same problem like Joanne and found the solution in the following thread: https://discussions.apple.com/thread/4890746
Sometime in the past I had SafariStand installed which needs SIMBL. After deinstalling SIMBL Safari worked fine again - Safari 5.1.8 ...
You might also try deinstalling Safari extensions.
Your reply helped to explore the problem, sadly I don't think its whats problematic on my machine. After I sent the inquiry I discovered that the update crash affected mail & addressbook too. After several phone calls with Apple, I now can't even log in. They recommend that I take it to the Genius Bar. In other words, after their directed help, I am a lot worse off. Will post all details in another question, just in case you or someone has another path to a solution without hauling it into the city.
Thanks for your help.
You're welcome -
I presume Apple support asked you to start the machine in 'Verbose Mode' or even in 'Safe Mode'?
You might use them for diagnostics and as well for saving your data.
I hope you will succeed -
Thanks for all of your helpful messages! Feels like a friendly world when my computer is acting decidedly unfriendly.!
I posted the whole list of what the Apple folks asked me to do under Macbook - app update failure.
last thing with those guys they asked me to do power up while holding the option key with the OS disc in the drive, selecting that. It didn't work immediately so they said, take it to one of the Apple stores.
Tried it again this evening and It did work so I guess I will call them again in the morning and see what it takes to re-install Snow Leopard. Hopefully my drive has not died.