The boot loaders usually suggested for Linux are LILO and Grub. LILO is beginning to show its age a little, but I still use it. Grub is newer, but it's ... well ... newer.

Important documents to read are the Multiboot-with-GRUB and Multiboot-with-LILO mini-HOWTOs.

You might also try looking at the Linux+Win9x+Grub-HOWTO, the Linux+NT-Loader mini-HOWTO, the Linux+Win95 mini-HOWTO, and the Linux+WinNT mini-HOWTO.