You need to devise a way for your server to determine what timezone the client is in. I once saw a site that claimed to somehow determine this from IP address alone (I don't know with how much accuracy), but the source wasn't available for it :(. JavaScript would be easiest, though somewhat of a kludge, because you would need two pageloads to get the timezone info back. An embedded Java app (blech) is another highly unrecommended approach, but it would take only one load.

An offhand idea: does anybody know if local times can be coerced from the client when it sends a cookie value back? I don't know of any such way, but if so, you could pull some magic by sending a cookie with the main page and then getting it back with a graphic on that page.