Maybe you should consider getting an upgraded version. Personally I dont trust invalid certificates. Must be because I work in a e-bizz security company providing CA solutions to banks and other third parties.

Then you should also know the prices of such a cert. Undernet is a network that lives from sponsoring providers that donate resources and does not generate any financial income as far as I know.
Maybe you want to donate the money for undernet to get a cert ?

Undernet has a registered copy of JAVirc (http://www.javirc.com)
but it has not been updated since at least 2 years, that explains that the
certificate is invalid. I would appreciate an update of the applet

- dp - (Former admin of caen.fr.eu.undernet.org)

i like the site just way it is