6. It is available here:
Go to http://java.sun.com/javase/downloads/index.jsp
Scroll down the page to 'Java Runtime Environment (JRE) 6' and press the 'Download' button.
Uninstall any previous Java versions from Control Panel, add-remove programs afterward.
Version 6 is only for Win2K onwards and includes Vista and 64 bit versions.
For 98/ME still need to use VERSION 5 UPDATE 10
PS - Thanks to Basementgeek to have pointed it.