Note that multiple operating systems booting on a single machine is still something of a black art. This document does not even attempt to document the various boot managers, which vary by architecture and even by subarchitecture. You should see your boot manager's documentation for more information.
If you have booted from SRM, if you select this option, the installer will write aboot to the first sector of the disk on which you installed Debian. Be very careful - it is not possible to boot multiple operating systems (e.g. GNU/Linux, Free/Open/NetBSD, OSF/1 a.k.a. Digital Unix a.k.a. Tru64 Unix, or OpenVMS) from the same disk. If you also have a different operating system installed on the disk where you have installed Debian, you will have to boot GNU/Linux from a floppy instead.
If you have booted from MILO, the installer will attempt to find a FAT-formatted partition and copy linload.exe and the MILO binary there.