The Tutorial link that BenderBot1138 supplies is more or less the same info as the stuff that was downloadable from the site you are trying to find...
I updated my FCP3 under OSX on my iBook-500 just for a laugh and it did indeed work!...Totally and utterly unusable really...the iBook was able to render very basic transitions (cross dissolve and wipes) in real-time, but as soon as it had finished the real-time sections it died completly and was no longer able to play standard footage from the time-line unless playback was stopped and started.
...so, it obviously does work, and will probably work slightly better on G4 machines...but it would seem Apple have set these levels for very obvious reasons!