If you have connected an  usb/serial cable for you raspberry, you probably want to avoid boot login, and automaticaly have a root autologin.

Two way to achieve your goal

1) The first and easiest is to install mingetty

$aptitude install mingetty

This following command is for Debian distributions (Squeeeze,Raspbians)

2) If mingetty are not supported by your distribution, you need to download and compil it like in this little Makefile:

MINGETTY_DONWLOAD_LINK=http://sourceforge.net/projects/mingetty/files/latest/download
BIN_DIR=your-rpi-binary-depository
ROOTFS=yout-rpi-filesystem

mingetty:
@(echo "installing mingetty binary in $(ROOTFS) directory")
@(wget --continue --tries=45 --directory-prefix=$(BIN_DIR) $(MINGETTY_DONWLOAD_LINK) --output-document=mingetty-1.08.tar.gz --output-file $(WGET_LOG))
@(tar xf $(BIN_DIR)/mingetty-1.08.tar.gz --directory $(BIN_DIR))
@(sed -i "s|DESTDIR=(.*)|DESTDIR=../$(ROOTFS)|" $(BIN_DIR)/mingetty-1.08/Makefile)
@(sed -i "s|CC=(.*)|CC=$(CROSS_COMPILE)gcc|" $(BIN_DIR)/mingetty-1.08/Makefile)
@(make -C $(BIN_DIR)/mingetty-1.08 all)
@(make -C $(BIN_DIR)/mingetty-1.08 install)


just use command:
$make mingetty
This will install mingetty in $(ROOTFS)/bin/
Now you just to configure init binary with file /etc/inittab, to use mingetty in order to have a root autologin
replace line : ‘T0:2345:respawn:/sbin/getty -L ttyAMA0 115200 vt100’ by

‘T0:2345:respawn:/sbin/mingetty –autologin root –noclear ttyAMA0 115200 vt100’
Reboot your raspberry and enjoy