Access mouse in fullscreen on X11?

Hello everyone,
I am using SDL with OpenGL. When I switch SDL_FULLSCREEN on with X11
on GNU/Linux (Ubuntu 9.10 Karmic with SDL 1.2.13) I lose the control
of my cursor! This kind of behaviour does not happen with GTK+
applications when in fullscreen mode, for example. If my application
is fullscreen on the screen :0.1, how can I be able to use my mouse
cursor in the screen :0.0?

Alexandre Quessy