@Cathy - my experience differs from yours.
on my first server, after installing the Safari 5.1.4 update, my Software Update application and command line refused to function properly, crashing, etc., as described in this thread.
I used Peter's method to change the gui application to launch Software Update in 32-bit mode, and it performed normally after that.
Today, I used Software Update running in 32-bit mode to install the Safari 5.1.5 update. After the reboot, verified that the current version of Safari was indeed 5.1.5. I then unchecked the "Open in 32-bit mode" checkbox in the Software Update Info panel. Software Update ran normally in 64-bit mode, and I used it in this mode to install the next two updates (Java Update 7 & iTunes 10.6.1).
so, for me, it appears that the Safari 5.1.5 update did indeed fix the problem with using Software Update application. I'll leave it in 64-bit mode and see what happens going forward.
note - @RobJensonCHS - I've seen Safari updates over the past year or so run, but after the Safari update ran (via Software Update application), my version of Safari had not changed. Typically a second round of running Software Update resulted in an updated copy of Safari, although at least once I had to run it 3 times!
cheers all!