Then you're in luck...

Apple currently has JDK 1.6 in development with no official word on its
scheduled release.  But all Mac OS X releases have included a JDK.  The
current version, Mac OS X 10.4 (aka Tiger), came (if memory serves) with
1.4 that was updated to 1.4.2 and later 1.5 became available...I may be
remembering that incorrectly.  But which specific Java you want may
depend in some part on whether you have a requirement to support
specific versions of Mac OS X.

I suggest visiting <http://developer.apple.com/java/> for a start.  
While Apple's JVM does in fact support Swing and all the usual stuff,
its UI and environment will need some extra steps if you want your
application to be able to act like a traditional Mac application -- one
that can be double-clicked, put a proper icon on the Dock, have a proper
name in the menu bar, etc.  But pure, unadulterated Swing will work and
simply not look quite like the norm.  You can find a wealth of
information starting there.  If you want more, you might want to
subscribe to the java-dev mailing list that's offered.  It's not too
high-traffic (though it has its days) and its archive is available to
search.  You'll find a link on that page for more on it.

= Steve =