Yes. JBuilder is available for more than just Windows but not all versions are available on all platforms. JBuilder 2007 is Windows only (till now). JBuilder 2006 runs on Linux and Solaris too. Only 2005 runs on Mac OS (doesn't say X though).
I would like to note thought that JBuilder 2007 is now based on Eclipse (looks exactly the same). You can think of it as Eclipse+Borland's plugins. I already got it at work but didn't migrate to it from 2006 yet.
You know you can modify your own thread titles don't you?
Also, I am curious if you must have JBuilder, or were you just looking for an IDE? A few others that run well in OS X include IDEA, Eclipse, and NetBeans.