It sounds more likely that your Network settings are out, rather than anything wrong with the Mac or Airport, and older drivers should be ok to at least get you online to update.
I don't know how much you know about Mac's, so sorry if this is obvious. Go to the Apple menu in the top left corner of the screen, and from there click on 'System Preferences'. When the preferences open, click on 'Network'.
Make sure you are connected by Airport rather than Ethernet in the settings, and where possible, use the Automatic settings.
There is an Assist button if you need help. Sorry, I don't know your ISP details so I really can't help you configure! You could try calling them, if they are Mac friendly they may be Airport savy and offer help. Be aware though that some ISP's will tell you that they don't support Airport and wireless with a Mac, well, they say that in the UK, but it dosn't mean you can't get it working, just they can't and won't help you to do it.
Sorry, not the best of help but I am sure when everyone wakes up one of them on here will have better advice!
Best of luck
Marc