PowerPC? Heh, I've still got a G4 lying around somewhere...
Unless
QLab is a universal
binary, you'll have to see if a legacy version has a PPC
build.
The last PPC version of OS X is 10.5, and requires it it to have a G4
processor of 867 MHz or higher.
The fact that it has 10.3.9 installed at the moment means uncertainty for if it meets the minimum requirements, as that sounds more likely to be a G3.