The biggest graphics benefit of jaguar is Quartz Extreme which requires an AGP graphics card with 32 megs of RAM and some compositing features. The Mobility 128 does not qualify. I do think there is better support under Jaguar for the Mobility 128 (I have the same iBook) but it isn't a night and day difference. There are however, more than enough other little improvements is jag to justify the upgrade. Not to mention that it is required for some of the new iApps and Safari.

-Mike