Opening an HTML file in Emacs automatically loads /usr/libexec/emacs/21.2/i386-redhat-linux/fns-21.2.1.el. If HTML -> View Buffer Contents is selected, it try to load netscape and fails because it is not included anymore. It should use htmlview to load the preview so it is not dependent on one browser.
Ok, browse-url now defaults to htmlview in emacs-21.2-33. Could you please confirm that this fixes the problem. This also affects XEmacs's browse-url.el - fixing that too in xemacs-21.4.12-6.
emacs-21.2-33 works fine now. Thanks for fixing it.