Not sure whether this is PowerPC specific or a more general problem, so I'm asking it to a general audience rather than Apple group.
I successfully installed 12.04 on a PowerBook G4 512M 1GHz 15", followed by installing firmware-b43-installer to get the wireless going.
I was exploring adding memory. I took out the memory cards to look at them and replaced them in their sockets. One of the 256M cards wasn't seated properly. When I rebooted, the system came up but was very sluggish, and after messing around a while, discovered the problem was having only 256M of working memory.
I reseated the memory card and the system came up fine with 512M of memory. However, wireless is no long active. I can't figure how to activate it. I think the Airport Extreme card may be turned off, but I don't know how to turn it on.