What is the master boot record (MBR) and why does LILO erase the old boot loader? Every hard drive has atop space called the MBR where the BIOS will try to load an operating system. Every system has its own loader. DOS has DOS-MBR, Windows NT has the NTLDR and Linux has LILO.
When you install LILO, you can install it in the MBR or in a boot record for the Linux partition. If you want to keep your current boot loader, you can select the Linux partition, and make sure it is the active partition in fdisk. This way you will be able to boot to LILO,and then boot the old loader from the MBR.
If you plan on only using Linux on your system, you can tell LILO to boot right into Linux and not display a
"boot:" prompt, and you can install it in the MBR.
"Linux Tips: Master boot record and LILO"