GRand Unified Bootloader
References to See on:
Wikipedia
Google Search
GNU Project
How-To's, Samples, etc... (Applies to other OS's besides Linux)
Full Tutorial at: Dedoimendo
"Legacy" version... w/ link to GRUB-2
Configuring the Bootloader ... at: gentoo.org
Covers: GRUB Legacy, GRUB 2, and LILO
:-)