I was the recipient of gift-giving gone awry. Well meaning, but unaware that Halo needed more than my <1 year old iBook has.
Crap, I thought and thought of returning it or waiting until my next Mac. Then, late last week, I decided to try it out. I loaded it up and set everything so the graphics we about on par with Doom 1

and played.
I was quite surprised that it played as well as it did! That is not to mean it is excellent, far from excellent, but playable? Pretty much. I finished it and there were some lags, but nothing too bad. 2 kinds of enemy weapon fire were too much for my 32MB video card and when I encountered said weapons, the screen would go dark.
That aside, it was playable. I should say that I have 640 MB of RAM, if that makes a difference. Maybe so. I didn't get the great graphics and it could have been faster. Overall, it played at about 17fps on average, according to the time demo. Nowhere near great, but I got to salvage a well-intentioned gift.