Do you mean using the PB's internal screen to display the PS3's output?
Yes, but not cheaply, and only (to my knowledge) with analog composite or S-video. No high-def digital.
You's need to buy a video-input device, and it has to be one without a delay or game-playing would be an exercise in frustration. Some ElGato devices offer near-zero image lag, for instance, and can be used with game consoles.
I have a USB EyeTV Hybrid, which I have used successfully with my PBG4 (1.25 Ghz, Readon Mobility 9600/64 MB). I think my PB is a bit below minimum stated specs for EyeTV, but it still worked.
But that's about $120 on Amazon. (It's also a digital high-def TV tuner, an analog TV tuner, and a DVR package.) Miglia TV Micro Express is cheaper but it most likely has a delay--you'd need to be sure about that before buying something.
Now, if you mean simply sharing the PB's Internet connection, that's a lot easier! Enable Internet Sharing, and open ports as needed or turn off the Mac firewall.