Some more findings. I set a different router as a bridge to my main router. I connected using Powerbook's wifi to the second router for the last couple of hours, and the system is rock solid. No freezes, no problems at all. I even downloaded multiple files, while I was listening online music.

It seems there is a serious conflict of Powerbook's wifi card with my main router. The next days I will try to find what the issue is, but I guess is a driver ruther than hardware problem.

Are there any log solutions to record what is happening on the machine while there is a crash?