Avast for Mac won't work in this "architecture"

I have a Mac G5. After downloading the program and placing it in the applications folder, I attempted to activate. Message said something like, “Can’t open in this architecture.” What does that mean and why won’t it work? Thanks!

Sorry, but only the Intel x86 architecture is supported in the new avast!, so it can not be installed on a G5 machine.

If you have a valid Avast for Mac License you can still download the older version that works on PowerPC here:
http://public.avast.com/~cimbal/avast.3.11.zip