lhoward is correct with his answer. To expand on that:
if you are using the CGI module (as you should) then you can output this type of header using
something like print header(-charset=>'big5').
A big reason why you need to do this is that the CGI module
by default outputs charset=ISO-8859-1; this
must be explictly overriden. You probably have seen that,
at least with your web browser, a META tag is not enough
to override it.