Solved! : Dell Vostro 3750 - touchpad detected only as PS/2 mouse
I've found the following website:
which led me to the following files:
I've installed the file http://people.canonical.com/~sforshee/alps-touchpad/psmouse-alps-0.6/psmouse-alps-dkms_0.6_all.deb
and now my ALPS touchpad works!
I think, that this patch should be included in Debian...