IF YOU HAVE THIS PROBLEM:

My Mac kept crashing about 5/6th of the way into using this upgrade. And I don't just mean that the installer crashed but that the whole computer crashed.

HOW YOU MIGHT WORK AROUND THIS PROBLEM:

Reboot your Mac. The instant the screen clears and the boot process begins, press down and hold down the "shift" key. I'm not certain when it is 'safe' to let up on the "shift" key so you might just want to continue holding it down until your Mac is 100% up and running.

Now run the Keyspan installer.

WHY IT WORKS:

I'm not sure. Someone who knows more about drivers will probably know but I'm guessing that because a "shift" boot causes the Mac to skip loading 3rd party software and drivers (presumably this includes the Keyspan drivers), the installer is able to cover the old drivers with the new versions without the added roadblock of having the older drivers running at the time. But that's just a guess. Good luck!