This guide will show you how to login to a Debian image and start LXDE by simply powering the Pi on.
Method 1: Auto Login:
In Terminal:
sudo nano /etc/inittab
Scroll down to:
1:2345:respawn:/sbin/getty 115200 tty1
and change to
#1:2345:respawn:/sbin/getty 115200 tty1
Under that line add:
1:2345:respawn:/bin/login -f pi tty1 </dev/tty1 >/dev/tty1 2>&1
Ctrl+X to exit, Y to save followed by enter twice
Method 2: Auto StartX (Run LXDE)
In Terminal:
sudo nano /etc/rc.local
Scroll to the bottom and add the following above exit 0:
su -l pi -c startx
(where pi is the username you want to run X as). Press Ctrl+X to exit, Y to save followed by Enter twice.
(Note: The previous method indicated that you should add startx to /etc/profile. The updated method is better, since it will cause startx to run only when necessary, and it will not launch the X server as root.)