i would like to make dual arch (amd64/i386) install DVD.

as both architectures uses exactly the same booting process i have to make 
boot image with two kernels and manual select it at boot loader

about 5.5 MB is required space so no floppy image is possible.
only -hard-disk-boot make sense.

and i tried to make hard disk image

dd if=/dev/zero of=hd.image bs=1m count=10
vnconfig -c vnd0 hd.image

and then - how to set up partitions with fdisk and disklabel?

tried different ways - no success. "no operating system" is the best 
result - as mkisofs reported no problems. or mkisofs reports geometry 
mismatch etc. installboot and fdisk -i were done (i think) properly.

or maybe bootloader can be started in -no-emul-boot mode and read kernel 
directly from cd9660 filesystem? freebsd does it that way. /boot has 
cd9660 support.