What do I need to surf via Wifi

Hello - I had a couple of bad false starts on setting up a wifi system with my Mac - I was told that the current airport and airport extreme that is sold now doesn't support my mac which is a G4 about 7 years old and has an Apple internal 56K Modem (v.90) - so my questions are - can I get an older airport (not crazy about this because I feel it would be slower) or can I get an updated external modem and attach it to my computer bypassing the internal one or can I get some kind of USB device that I can plug in - Thank you