Note that both fdisk and disklabel have "partitions", but they
represent different things. fdisk creates what you call "slices".
NetBSD can only easily use one of them. disklabel creates partitions
in the traditional BSD sense. These are supposed to live within a
single fdisk partition. However, you can cheat by adjusting the
disklabel numbers (start and offset) to point outside the NetBSD fdisk
partition. BTW, this is also how you would access fdisk partitions for
other operating systems (i.e. Windows). Hope I haven't confused you
too much.