I'm close to the solution.

If I run glxinfo | grep renderer as root, I get

direct rendering: Yes
OpenGL renderer string: Mesa DRI Mobile Intel�� GM45 Express Chipset GEM
20090114


while, if I run the same command as a simple user, I get

direct rendering: Yes
OpenGL renderer string: Software Rasterizer

So I think that's a permission problem now.

Have you any idea?

Thanks a lot,
Massimiliano