I would suggest installing a snapshot of 4.0_BETA2.  See
http://www.netbsd.org/docs/current/ for where to get them.

Today, look in

ftp://ftp.netbsd.org/pub/NetBSD-daily/netbsd-4/200708040002Z/iso/

This is the contents of the netbsd-4 branch from two days ago.  Since
you are intending to learn rather than set up a production server, there
aren't really any good reasons to stay on the stable branch.