If Ubuntu Hardy is your favorite system, then you can very easily install NetBeans IDE 6.0.1 on your machine via the Synaptic Package Manager. Invoke System -> Administration -> Synaptic Package Manager and search "netbeans" in the available packages.
The distribution contains the NetBeans Java SE 6.0.1 distro. Missing features like Web&j2EE and Mobility can be installed from the NetBeans Update center (click on Tools -> Plugins and choose Available Plugins tab). The package has a dependency on OpenJDK, which is a fully buildable Java Development Kit based completely on free and open source code.
The NetBeans project is looking for people to use this NetBeans 6.0.1 distribution with OpenJDK on a daily basis. To pass on feedback and if you encounter issues, please report them to NetBeans Issuezilla.