The Java SDK for Macintosh version 6.0 and the NetBeans IDE for Macintosh must be downloaded and installed separately. There is no combined download package for this combination of Java version and NetBeans IDE.
Downloading the Java software
Java 6.0 for Macintosh is only available (as of December 2006) as a Developer Preview. You must be an Apple Developer Connection member to download this software. Go to the Apple Developer Connection Java SE 6.0 Release 1 Developer Preview 6 site and either Sign In or Sign Up for a free memebership to download the software.
Downloading the NetBeans software
Go to the NetBeans IDE 5.5 Download page and click on the "Mac OS X" link in the "NetBeans IDE 5.5 Download Installers" table. The download should begin automatically.
Installing the NetBeans Software
After downloading the software bundle, the installation instructions for this package can be found on the NetBeans Community web site here (you must scroll down to see the Macintosh installation instructions).