Netbeans is based on Swing, and Swing supports several Look and Feels. I already tried with Netbeans 6.0 or 6.1 to change the default Look and Feel to Nimbus - but it didn't worked in the past. With Netbeans 6.5 it is surprisingly easy to switch to Nimbus. You only have to provide the argument:--laf Nimbus. You can provide the parameter at start (e.g. netbeans.exe --laf Nimbus), or extend the [installation]/etc/netbeans.conf. There is a short tutorial available as well.
Netbeans looks really good with Nimbus running on Vista. Netbeans 6.5 with Nimbus is available with JDK 6 update 10+ running on Linux, OpenSolaris, Windows and Mac OS X. In the past I switched between Eclipse and Netbeans back and forth and enjoyed the different UI, behavior and art work. Now I can stay longer in Netbeans :-).