Marc Liyanage has created a small Cocoa app that checks if the machine is using Quartz Extreme in Mac OS X 10.2 Jaguar.
Quartz Extreme uses a supported (see below) graphics card built into your Mac to relieve the main PowerPC chip of on screen calculations. This dramatically improves system performance, making Jaguar much more responsive. Quartz uses the integrated OpenGL technology to convert each window into a texture, then sends it to the graphics card to render on screen. The graphics processor focuses on what it does best ? graphics ? freeing the Power PC chip to do more operations in the same amount of time. Everything is zippier.
Quartz Extreme functionality is supported by the following video GPUs:
NVIDIA GeForce2 MX, GeForce3, GeForce4 MX, or GeForce4 Ti or any AGP-based ATI RADEON GPU. A minimum of 16MB VRAM is required.
More info and download link here.