I just checked the system requirements for Print Shop 2 for the Mac. There seems to be some conflicting statements made by the publisher. They're claiming it can be installed on PPC machines (G3...) and then go on to say it will even work with Mountain Lion. Lion and Mountain Lion can no longer run an application which is PPC coded. Mountain Lion is Intel only.
I would get in touch with the publisher (MacKiev) and try to find out what's going on. Also, if you need a program to do greeting cards, flyers, brochures, etc, Apple iWork Pages in layout mode can do all of that. It's only $19.99 and comes with a myriad of nice templates.