Actually, my card works perfecty with windows.
With knoppix distrib, it (almost) works with vesa driver on low resolutions, 800x600 I guess, but I still can't get it to work on a better resolution, and it still doesn't work with my distrib.
The point is that I tried with a previous kernel version (2.4.19, I'm using 2.4.22) and it seems to work better in console mode, because some better video modes are working (better than 80x25).
Since I'm not really understanding what I'm doing and I don't understand why the kernel version should really matter, I don't know what to do.
The alternative is to reinstall linux (?)