Just went through this myself, the NetBSD webpage has a good FAQ on it.   
http://www.netbsd.org/Ports/i386/faq.html#msdos_partition given it's from   
the i386 port FAQ, it should work the same.

John A. Maier
Kemper Military School and College
Director of MIS
Voice: 660-882-5623
Fax: 660-882-3778
Email: johnam@kemper.org
Web: www.kemper.org