nouveau, the project for creating a free 3D linux driver for nvidia cards, recently got first support for real 3D applications with gallium on some NV4X cards (see Nouveau Companion 36). Today I got it working on a friends machine.

Here you can see an openarena benchmark (also uploaded on youtube). It got 55 fps, which is far away from the nvidia binary driver yet (178 fps), but at least more than my r200 setup (32 fps).

For the brave ones, here's a quick and dirty howto for Gentoo:
a) Get the nouveau overlay with svn co https://svn.hboeck.de/nouveau-overlay and add it to PORTDIR_OVERLAY in make.conf.
b) The nouveau-overlay won't install the nouveau/gallium-branch of mesa. Get my overlay with svn co https://svn.hboeck.de/overlay and also add that to your PORTDIR_OVERLAY (I'll try to contact the nouveau-overlay developer if we can merge this).
b) Add media-libs/mesa, x11-base/x11-drm, x11-libs/libdrm and x11-drivers/xf86-video-nouveau to /etc/portage/package.keywords and merge them.
c) If you've been running the nvidia binary driver, eselect opengl set xorg-x11, change the graphics driver in xorg.conf to nouveau, rmmod nvidia (if you've been running the binary driver), modprobe nouveau and start X.
d) Have fun!

Note: The nouveau developers consider gallium completely unsupported at the moment and don't want to get end-user bugs. If it runs, fine, if not, don't nag them with it.

Binary drivers are imho a hughe problem for free software. Nvidia, leading graphics company, has produced binary linux drivers for a long time and there was no way to get free software 3D-support on their cards.
A group of people is working at the moment on a free nvidia driver, the project is called nouveau. I now had a chance to test the nouveau driver on a nvidia card (nv43). It doesn't do much at the moment, but at least it runs glxgears almost smooth.

It's nice to see development on that front. We made a small video of glxgears running on nouveau. Oh, for all those who can't play theora, I put it up on youtube (but seriously, was just curious how youtube works and if it accepts theora).

Some experimental nouveau-ebuilds, maintained by pq from the nouveau-project, are here:
svn co https://svn.hboeck.de/nouveau-overlay