I'm currently running Ubuntu in VirtualBox under Windows Vista. I've installed Putty and Xming, and can get an SSH connection into the Ubuntu virtual machine. 2d graphics work, so I assume xming is set up correctly, however I'm unable to get glxgears or Extreme Tux Racer to run.

I've tried both the normal Xming and the Xming-mesa install.
Glxgears errors out with
Error: couldn't get an RGB, Double-buffered visual

And ETRacer errors out with

*** etracer error: Couldn't initialize video: Couldn't find matching GLX visual (Resource temporarily unavailable)

They run locally in the virtual machine, so I don't see why they shouldn't run in Xming. Any ideas?