Did you know some Mac PowerPC applications that are designed to work with Mac OS X 10.5 or earlier won't run in 10.6 or later, without setting one or two options related to the application with the Finder?
This news comes from John Carter. He adds, "You have to have Rosetta installed on your computer, as it may be required to run that application. Rosetta is an optional application that you can install from your Mac install DVD (see this).

Show 'Get Info' for the application with your Finder. I'll use Safari as an example here:

Notice at the bottom of the image to the left there is a box to open Safari in 32-bit mode. Below that is a box to open using Rosetta Both of those boxes may have to be checked to run some PowerPC applications on 10.6 or later."