AIGLX is a extention to X.org X server that allows indirect 3d hardware acceleration.
It is supported by (the very latest) Nvidia propriatory drivers, R200 and R300 Free software ATI drivers (for ATI R200, R300, and R400 cards numbered 8500 thru X800), and the Free software Intel 915 drivers for pretty much all recent Intel integrated drivers.
The major drivers that do not support AIGLX at this time are ones are propriatory ATI drivers that support R300, R400, and R500 series cards.
For those, and as a option for Nvidia's propriatory drivers, you can use Novell's XGL (or more properly called XGLX) for similar effects.
Essentially AIGLX provides the basis for accelerated 3D compositing features ala Apple's Quartz Extreme for their Aqua interface, or Microsoft Vista's new Areo interface.
hehe.
And yes, Ubuntu is going to be your best bet. Also Suse/OpenSuse is worth a look at and so is Fedora Core 6.