From: "Brad Tilley" <b...@16systems.com>
as appropriate if you're using grub etc or XP..
Another Option. Assuming a i386 or amd64 PC:
1. Put another hard drive into the computer.
2. Go into the BIOS and make the new hard drive have higher priority.
3. Boot the computer and install OpenBSD onto the new hard drive (Run
dmesg to be sure you're doing the right thing)
4. When you want to go back into the other OS, change the drive priority
in the BIOS and reboot.
Not pretty, but it works and keeps drives separate and no fooling with
grub, partitions, Windows boot loader, etc.
If you're going to take /that/ approach, I would suggest a trayless SATA
caddy from someone like Icy Dock (be careful - some of their products are
garbage, but I can attest that the trayless, fanless SATA caddy is not).
You can easily swap the drives in and out without faffing with BIOSes.
I use precisely that method for swapping in test systems.