I've got one of those lying around... I agree with what Zen said, and I'll add that Unreal Tournament to the games that would play well, and UT 2004 to the ones that can play fairly well on low quality.
Halo is great. I'm amazed at how well it plays on the iBook with all settings maxed.
I'm playing the demo currently, can that be updated?
The game requirements for H1 are G4 800MHz and a Radeon 7500. Your iBook goes well beyond that with the 1.33GHz and Radeon 9550.
Minimum requirements are just that-- minimum requirements. Things will be (mostly) playable at low settings. It says nothing about how well it will perform at its highest settings.