Using a boot manager to choose the BeOS from the list of operating systems installed on your hard drive(s). This option gives you the most flexibility, and is the ideal way to boot the BeOS.
Be provides a basic boot manager with the BeOS. You can find the shell script which installs it in the /optional/experimental/scripts folder.
You can also boot the BeOS using commercial boot managers, such as System Commander, the boot manager that comes with PartitionMagic, or the Windows NT boot manager.
The BeOS is also compatible with LILO, the Linux Loader, so you can use that as well (though we won't provide support for LILO; we assume if you're using it, you know what you're doing). You can find far more about LILO than you could ever possibly want to know in a recent Be Newsletter article, "Booting Variations For PC And LILO":
http://www.be.com/aboutbe/benewsletter/volume_II/Issue15.html#Insight
At Be, we've successfully used the Be boot loader, LILO, the Windows NT loader, and System Commander, and we've received reports of other solutions that work fine for other people.
System Commander is a particularly fine product, especially the Deluxe version. Version 4.01, shipping now, even provides specific support for the BeOS, correctly identifying BeOS volumes (earlier versions still work, they just don't identify Be volumes by name).
If you have more than two operating systems on your system, it's probably the best solution available, and well worth purchasing. See the VCOM web site for more details:
http://www.v-com.com/