[kh99]

They are available as $thread[dateline] and $thread[lastpost], but they are unix timestamp format, so you'd need a plugin to format them like you want them. I think you could use a plugin using hook showthread_complete and code like this:

$published_time = date(DATE_ATOM, $thread[dateline]);
$modified_time = date(DATE_ATOM, $thread[lastpost]);

then use $published_time and $modified_time in the SHOWTHREAD template.