Aha... (got there by link). It doesn't work on ATI cards, sorry :( Nothing to do with general system specs, just videocard and drivers. Try installing latest driver for your videocard, might help. It uses opengl for rendering, and nvidia is sorta better at opengl support. I only have GeForce FX 5200 and don't really know why it doesn't run on ATI videocards.
Maybe i'll try changing something. Strangely, with certain OpenGL drivers, sometimes little changes make it work or break it.
BTW you might find my mojoworld/volumetrics pages interesting.