Not true. It will not work with any website. Some forums use a different code.
If you go to a forum not using vBulliten or site like myspace.com, it will not work. All the codes should be displayed on the site somewhere. For instance, here you can find this little handy page- http://www.lucasforums.com/misc.php?do=bbcode
By the way, if you type a url such as www. lucasforums.com (without the space), the site will automatically make it a link.
@ RedHawke (Below)- Never noticed that. Learn something new everyday.