I have installed the new debian squeeze and to get my 3 displays working in the right way i have to install the nvidia driver.
Enter in terminal
#su
password
#nano /etc/apt/sources.list
add
deb http://debian.hands.com/debian/ squeeze main non-free contrib
deb-src http://debian.hands.com/debian/ squeeze main non-free contrib
press control + X
Press "y" to save
then
# aptitude install module-assistant nvidia-kernel-common
# m-a auto-install nvidia-kernel
# aptitude install nvidia-glx
# aptitude install nvidia-settings
# aptitude install nvidia-xconfig
# nvidia-xconfig
reboot
enter nvidia-xconfig as root and edit setting save to X configuration file
exit x
and enter!