Add to top of grub's menu.lst to enable serial console for grub. unit refers to the 'COM' port number.

serial --unit=0 --speed=9600
terminal --timeout=10 serial console

Add to kernel line:

console=tty0 console=ttyS0,9600

update /etc/inittab

s0:2345:respawn:/sbin/agetty -L -f /etc/issueserial 9600 ttyS0 vt100
s1:2345:respawn:/sbin/agetty -L -f /etc/issueserial 38400 ttyS1 vt100

Enable root login from serial console by updating /etc/securetty

ttyS0
ttyS1