thanks very much for the responses :-)
i think that... i don't have any control whatsoever of the university firewall... and i think it is the case that... the university firewall is blocking the chat :-(
i do have my windows firewall turned on, but if i turn it off i still can't chat.
i do have the latest version of java.
i think the situation is that i can chat okay from the office because the internet is by way of plugging it into the wall (sorry - dunno more than that)
whereas from home there is wireless access and they are blocking more sites because they are trying to be careful with how much bandwidth people are using up.

so... no chat from home :-(

thanks for all the help people