Bordermaker requires Java 6 and Apple has been lagging behind on that.
It all depends on the version of Mac OS X you are using. A summary:
Starting with the latest and the greatest: Snow Leopard (10.6) has
Java 6 built in (both 32 and 64 bit). I use it on my (older) Intel
MacBookPro and can simply doubleclick the bordermaker.jar. This is
your best bet :-)
If you use Leopard (10.5), you'll need to update Java (http://
support.apple.com/kb/HT2733), but then it should work.
If you use Tiger (10.4), you're on your own :-(
I guess there will never be an official Java 6 release for this OS X.
There are two alternatives however: The first one is SoyLatte (http://
landonf.bikemonkey.org/static/soylatte/) and the second one is a
'Apple Developer Connection Developer Preview' of Java 6. The first
one I didn't touch, but tinkered with the second. Our Semantica DMS
webapplication relied on Java 6 for a couple of applets and they
worked using this developer preview, so Bordermaker should do so as
well. I don't know if there's a copy of it still lingering 'round the
internet, but I probably stashed it somewhere on my Time Capsule, so
drop me a line if you need it and I'll make it available to you
somehow.