Well as your G5 doesn't have an airport card, the only way to go about things would be to wire your router to the G5 and also have a wireless signal going to your Xbox and PS3, since those do have wireless cards.
Or... I see. You could also create a wireless network from your wired G5 to send out a wireless signal to your router which would be connected to the game consoles. The G5 is capable of creating a wireless network, while the consoles, I presume, are not.
In any case, the G5 will have to be wired, because it doesn't have an airport card.
Is that right? I don't know if I completely understood your situation or not...
irmongoose