do a search for "boot fix for FreeBSD 4.0" ... essentially you have to use the tab key trick to get the screen to the bios text mode screen (I hit tab till I see the bios boot screen)
also, after you get running, you'll need to do the following to enable the usb on the box.
config -ef /bsd
all in all OpenBSD 2.8 was an easy install (even for a bsd newbie like myself).
P.S. thanks go to the openbsd mailing list for help on the enabling of usb ...