Yes, if your PowerPC has an AirPort card it will work with any AirPort base station. If it has an Ethernet port it will work with a wired network also.
Since the old PowerPC will use only 2.4 GHz you should use a dual band (5 GHz / 2.4 GHz) wirelss router. Otherwise your new MacBook Pro will be limited to 2.4 GHz also.
Thanks for the information.
My G4 does not have an airport card but it is connected to an Ethernet switch which has two printers plus the DSL modem attached to it. I am looking at a Linksys dual band Gigbite router which has four Ethernet ports plus a USB port. It has to be configured with the laptop with Mountain Lion. Will one of the ports on the router still allow the G4 to connect to the internet?
... Will one of the ports on the router still allow the G4 to connect to the internet?
Yes. Ethernet is simple. OS X constantly and relentlessly searches for any network connection it can find. Plug it in and it will work.
Are you considering the Linksys EA3500 or something similar? Get what you want but be sure to read its reviews first. In my opinion Linksys consumer grade products suffered after Cisco's acquisition of them, and their customer support went from poor to abysmal.
A genuine Apple AirPort Extreme Base Station is more expensive, but not much more so. Its advantage is the ability to be configured with AirPort Utility whereas other routers either use dedicated Windows software or a browser interface. Read its reviews too then decide for yourself.
If you already have an Ethernet switch the additional port of the EA3500 is superfluous. You could just as easily use the less expensive AirPort Express, $99 before discounts. It has almost all the features of the Extreme including simultaneous dual band wireless, and in addition can also stream iTunes music to remote speakers through its audio port. The major difference between the Extreme and the Express is the latter's lack of additional LAN ports, so just use your switch.
All AirPort Base Stations support printing through their USB port, and all are guaranteed to be compatible with AirPrint should you ever need to.