Absolute OpenBSD: Unix for the Practical Paranoid

Careful planning is essential when installing two operating systems on a single hard drive. Each operating system has restrictions on where it may lie on the disk, and you must satisfy those restrictions for every OS you install. For example, Windows 98 expects to be the first operating system on the disk, but OpenBSD's root partition expects to be within the first 8GB. This can make life difficult. Consider the restrictions on each operating system, and figure out a method you can meet them while still getting both operating systems on one drive. Write down your partitioning needs before starting an install.

You then need to create MBR partitions for each operating system, using the appropriate tool for that OS. Once you know where these MBR partitions belong, you can start to install your operating systems. Operating systems should be installed in the order that they go on disk — if Windows XP is the first operating system on your disk, install that first. This allows you to use each operating system's native tools to create the MBR partition for that operating system. Not all operating systems work well within MBR partitions created by another operating system: For example, the Windows XP installer will see partitions created by OpenBSD, but may choke when attempting to put a file system on them.

Once you have all of your operating systems on the disk, install a boot manager to control the OS you want to start at boot time.