Identifying PowerPC applications that will not work on OS X releases beyond Snow Leopard?
I don't have a Snow Leopard install handy but this info is available in System Profiler...

Apple Menu > About > More Info

In the resulting app there should be a way to view the installed applications.  In that list there will be a column "Kind" that will state "Intel", "Universal" or "PPC".

Screen shot of how this looks in Mountain Lion: (may look different in Snow Leopard, but idea is the same.)