Grub configuration

In grub configuration, you could have a lot settings for OS.

here is an example of /boot/grub/menu.lst file

#boot=/dev/sda  // comments

default=0  // default loading OS

timeout=5  // timeout 5 seconds before getting into default OS

splashimage=(hd0,0)/grub/splash.xpm.gz 

hiddenmenu

title CentOS (2.6.18-194.17.1.el5)

    root (hd0,0)

    kernel /vmlinuz-2.6.18-194.17.1.el5 ro root=/dev/VolGroup00/LogVol00 rhgb acpi_sleep=s3_bios quiet

    initrd /initrd-2.6.18-194.17.1.el5.img

title CentOS (2.6.18-194.el5)

    root (hd0,0)

    kernel /vmlinuz-2.6.18-194.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet

    initrd /initrd-2.6.18-194.el5.img

For example, you could set the serial port setting.
You could add it at the kernel section.
You also can add something like acpi_sleep=s3_bios at the kernel line.

more detailed about serial port: 
http://tldp.org/HOWTO/Remote-Serial-Console-HOWTO/configure-kernel-grub.html