If you're the one developing the software, you can add "BuildMax = 0xC0000000" to the [CEDevice] section of the installation .inf file before creating the .cab file. If you're not the developer, and you just want to disable it on the PPC, I'd guess there might be registry entry... But then, how many programs are you installing that this is such a terrible annoyance that it needs to be disabled?
-John