GRUB stands for GRand Unified Bootloader and is the default bootloader for Linux RH8x and RH9. GRUB is designed to load a variety of operating systems. GRUB supports chain-loading that allows loading both the Linux boot loader and the boot loader of another system such as the one required by Windows.
GRUB is dynamically configured through its configuration file and does not require MBR re-writing at configuration changes, ex. when a new module is added. GRUB can be changed at startup through the edit facilities and the boot loader commands.
GRUB documentation is available at /usr/share/doc/grub-version and at the following sites:
http://www.gnu.org/software/grub
http://www.uruk.org/orig-grub
http://www.redhat.com/mirrors/LDP/HOWTO/mini/Multiboot-with-GRUB.html/
http://www.linuxgazette.com/issue64/kohli.html