Thanks for the replies. It grumbled a bit about different versions like:

pkg_add: Warning: package
`ftp://ftp.NetBSD.org/pub/NetBSD/packages/3.0/i386/All/kde-3.5.3.tgz'
was built for a different version of the OS:
pkg_add: NetBSD/i386 3.0 (pkg) vs. NetBSD/i386 3.1 (this host)

But then failed to find some packages, which I presume is more serious:

pkg_add: no pkg found for 'qt3-libs-3.3.6nb1', sorry.
pkg_add: 1 package addition failed
pkg_add: autoload of dependency `qt3-libs>=3.3.6nb1' failed!
pkg_add: no pkg found for 'qt3-libs>=3.3.6nb1', sorry.

And failed for these too (with similar lines around the autoload line):

pkg_add: autoload of dependency `arts-1.5.3nb1' failed!
pkg_add: autoload of dependency `arts>=1.5.1nb1' failed!
pkg_add: autoload of dependency `kdelibs-3.5.3' failed!
pkg_add: autoload of dependency `kdelibs-3.5.3{,nb[0-9]*}' failed!
pkg_add: autoload of dependency `arts-1.5.3nb1' failed!
pkg_add: autoload of dependency `kdebase-3.5.3nb1' failed!
pkg_add: autoload of dependency `kdebase>=3.5.2nb2' failed!
pkg_add: autoload of dependency `kdelibs>=3.5.2nb1' failed!
pkg_add: autoload of dependency `kdeaccessibility-3.5.3' failed!
pkg_add: autoload of dependency `kdeaccessibility-3.5.3{,nb[0-9]*}' failed!
pkg_add: autoload of dependency `kdeartwork-3.5.3' failed!
pkg_add: autoload of dependency `kdeartwork-3.5.3{,nb[0-9]*}' failed!

It seemed to get in a loop of reporting the same failures, while still
downloading, so I stopped it with ^c.

I'll try to build the missing dependencies from source tomorrow.

-- 
John.