> (The extended partitions were made under Debian Linux. I don't know if
> they were created correctly.)

I haven't seen the output of fdisk for a system with many
extended partitions, but that does look (like what I thought was)
correct.

In particular each 'extended' partition should only contain 1
real partition and another extended one.
This makes it possible to edit, since the extended partion is set
up as if it were a header on the real partition and not as part
of some massive recursive structure.
> 
> What is the correct tool for easily reviewing, modifying or creating
> extended DOS partitions?

not netbsd :-)
 
> On this disk with an old BIOS with 1024 cylinder limitation, I plan to
> have three bootable different operating systems (all sharing /home and
> swap). To take advantage of entire disk I (believe I) need to use extended
> partitions. Any hints?

Well netbsd doesn't use the bios table at all, just the absolute
sector numbers in its disklabel.
You do need a small partition - it needs to contain /boot and
/netbsd.  If you build a kernel that has the root device built in
then the root filesystem can be elsewhere.
(I don't recall it being possible to read the kernel from a different
filesystem from the one that /boot (aka biosboot.sym) passes in as
the default root device.)

	David

-- 
David Laight: david@l8s.co.uk