OpenBSD doesn't distribute the ISO. You don't need it to install, though. If you have a network connection, just download the floppy boot file of choice and rawrite it (or dd it) to your floppy and boot from that. If you have a second computer and want to shorten the install time, download everything in advance and set up your own FTP server and point the network install to your box instead of one of the defaults. The install documentation for your particular platform (guessing it's i386) is laid out step-by-step and well documented.