Well this doesn't sound like any fun: enough Intel Macs running 10.4.8 must be having a problem connecting wirelessly to some 3rd party routers that Apple had to publish a support doc on the topic. As icing on the cake, Apple's solution isn't a pretty one either. If your Intel Mac is having this problem, here's Apple's solution: restart the router. If that doesn't fix the problem, Apple then recommends calling the router's manufacturer to spend 45 minutes on hold, getting tossed around between operators who probably dish out the same troubleshooting technique, just like the books taught 'em.
Not exactly the most effective solution I've ever heard to a problem like this, but I guess one must take what one can get - at least until one can download Mac OS X 10.4.9.