Ubuntu doesn't recognize my synaptics touchpad (regresion)

[cman]

Binary package hint: gsynaptics

My touchpad had always worked as a basic touchpad (without scroll function or any other extra) and i have never worried about it, but when i installed ubuntu intrepid ibex beta, suddenly it worked, i mean, with scroll function and everything!..
Then i update my laptop with the update manager and in this update i could see that update-manager wants to remove a package called "xorg-synaptic" or something like that... i updated it anyway and now my touchpad again doesn't work properly! and today i have installed gsynaptics and if i try to open the touchpad tool (system-->preferences-->touchpad) it says: "GSynaptics couldn't initialize. You have to set 'SHMConfig' 'true' in xorg.conf or XF86Config to use GSynaptics".

In my xorg.conf i can see just one mouse and i don't know if it is the touchpad or the usb mouse... also i don't know why should i modify now the xorg.conf if before everything was automatic!..

Finally I think that maybe it is related with the instalation of the propietary NVIDIA driver (maybe it changes my xorg.conf??)