The Java SDK for Macintosh version 5.0 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
If you have a Macintosh with a PowerPC processor (PPC) go to the Apple - Support - Download - J2SE 5.0 Release 4 (PPC) page and click on the "Download" link. If you have a Macintosh with an Intel processor go to the Apple - Support - Download - J2SE 5.0 Release 4 (Intel) page and click on the "Download" link. After clicking on the link, the download should begin automatically. The download is either 53 Megabytes (PPC) or 80 Megabytes (Intel) in size.
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).