As many others have suggested before, TenFourFox is the best web browser available. It's essentially FF4, just tuned for G3, G4, and G5 processors. It's been running beautifully on my G5.
As for video... well, it's an iBook, so you might want to look into Mactubes. Flash video may be choppy, so make sure you set it up to play videos with Quicktime, as this seems to have helped performance with others. Don't expect HD video playback, however...
Also, block Flash whereever you can! ClickToFlash and Flashblock are essentials even on Intel machines! They'll allow you to view flash content you intend to with a simple click, yet keep the annoying advertisements from loading and keep things from slowing down.