> 
> Imagine a machine which can't boot from CD, and has no floppy drive.  However,
> it has a functional network interface under DOS.  Can I install NetBSD on
> this?
yes. make dos partition with size equal to planned swap size (or shrink it
with some tool), ftp base.tgz, etc.tgz and netbsd.INSTALL (ungzipped) 
and dosboot.com, do dosboot netbsd.INSTALL

then run disklabel, create b partition in plase where dos partition exist,
a partition at rest (or maybe more partition if you like), newfs, untar
base.tgz, etc.tgz, installboot and OK