Thanks so much for the reply.

When I set up my new Mac, it asked if I wanted to install from a backup. I clicked yes and all my applications, files and internet settings installed with no problem from my external. Since I knew my hard drive was having problems, I copied AND backed up all the files onto two external drives.

I imagine some of them were messed up and are interfering with the new files for Snow Leopard. I repair permissions every time I install or upgrade something.

This latest Apple software update had problems installing two files and it seems strange that this would happen on a new computer. What do you think?