Client Viewer Software
Panotools Java Applet
There is an Open Source java applet in the original [Panotools] distribution. It works in most java enabled browser, including those with the real JVM from Sun and those with the bad Microsoft implementation.
expensive and not recommended!
Immervision has a free java applet with directionnal sound, animation and other advanced features which work with all JVM since version 1.1 (including IE and netscape ones). At this time this viewer is in Beta test version. (Applet Page)