I upgraded from Debian Etch to Lenny and recently I wanted to change my video driver and noticed that the new xorg.conf is the missing "driver" section and missing lot of sections.Where are the driver/resolution selection,monitor configuration,mouse configuration and all other sections gone?

Here is my new xorg.conf

Section "InputDevice"
Identifier "Generic Keyboard"
Driver "kbd"
Option "XkbRules" "xorg"
Option "XkbModel" "pc104"
Option "XkbLayout" "us"
EndSection

Section "InputDevice"
Identifier "Configured Mouse"
Driver "mouse"
EndSection

Section "Device"
Identifier "Configured Video Device"
EndSection

Section "Monitor"
Identifier "Configured Monitor"
EndSection

Section "Screen"
Identifier "Default Screen"
Monitor "Configured Monitor"
EndSection

As new versions come out, Xorg is capable of autodetecting more and more stuff. The resposible for that, to a big degree is the adoption of HAL. However, you can still write your own xorg.conf file if you want, I do.