I've been using 11.04 and its betas for a while now, and MegaGlest works well on it for me. Others have reported success in running MG on it, too.So I assume the issue you are reporting is indeed related to your hardware.
You can run MegaGlest from a terminal window to get more information on what exactly is going wrong. If you have the 64 bit (x86_64/amd64) variant of Ubuntu 11.04 then run this command before starting the game:
ulimit -c unlimited
This way, when it crashes, it creates a 'core' file in the current working directory. You can then upload this file on some free upload site and post the URL here, so I can inspect it further.
Whatever variant you have, the terminal window may display some error information you could post here, or better yet, to the MegaGlest forums.