Sometimes it is impossible to access the update center (for 5.x) or plugin manager (for 6.0) right from the IDE, for instance because of strict firewall rules. I discovered today that there's another way how to obtain the nbms and browse the contents of the update center - you can do it using your web browser!
The (no longer) secret URL to browse the plug-in repository is here: http://www.netbeans.info/uc/show_uc_content.html
Thank's Roumen. I'm always happy with every new post from you.