If you want a different appearance of NetBeans than it is the native one you can simple change the look and feel (L&F). There can be also another reason for changing look and feel due to a bug in Windows L&F. When you are on Windows machine and you use the native Windows look and feel you can run into a problem with focus. Switching between NetBeans IDE and for example Firefox using Alt+TAB and sometimes when switching back to the IDE instead of being focused in the editor where you left it, the menu is focused instead.
Some L&Fs are available in Sun Java and many L&Fs are available on internet. Using L&Fs that are in Sun JDK is simple. You should know which Java you use and which version. For example Nimbus L&F is available from Sun JDK 1.6. You can run NetBeans with this L&F in two ways. The first one is running NetBeans from command line with --laf option. This way is sufficient, if you want to just try a L&F. So on \*nix OS it's :
/path_where_netbans_are_installed/bin/netbeans --laf com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel
The second way is put the --laf option to the netbeans.conf file. The netbeans.conf file is located in etc folder in NetBeans installation folder. Open the netbeans.conf file and add the option into netbeans_default_options. When you do it in this way, then it's permanent and NetBeans will always start with this L&F.
There are a few screenshots of NetBeans with some L&F, which are available in Sun JDK 1.6.
Nimbus: --laf com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel
Metal: --laf javax.swing.plaf.metal.MetalLookAndFeel
GTK: --laf com.sun.java.swing.plaf.gtk.GTKLookAndFeel
As I wrote above, we are not limited only with L&Fs, which are available in a JDK. You can dowload different L&Fs from net. Some of them are open source and free, but there are also commercial. If you want to use such L&F, you have to download a jar that contains the L&F definition and put it on NetBeans classpath. When you want to try a L&F on the command line, then you run NetBeans also with -cp:p path_to_L&F_jar option, which adds the jar on the NetBeans classpath. For example the command for using Liquid L&F will be:
/path_where_netbans_are_installed/bin/netbeans --laf com.birosoft.liquid.LiquidLookAndFeel -cp:p /path/to/liquidlnf.jar
You can put both options into default netbeans_default_options in netbeans.conf file, if you want to use command line.
There are a few examples. You can download the jar from the projects page and play with them.
Liquid: --laf com.birosoft.liquid.LiquidLookAndFeel -cp:p /path/to/liquidlnf.jar
Napkin: --laf net.sourceforge.napkinlaf.NapkinLookAndFeel -cp:p /path/to/napkinlaf.jar
NimROD: --laf com.nilo.plaf.nimrod.NimRODLookAndFeel -cp:p /path/to/nimrodlf.jar
Quaqua: --laf ch.randelshofer.quaqua.QuaquaLookAndFeel -cp:p /path/to/quaqua.jar
If you find a nice L&F, write me, I will add the screenshot here.