honestly: your code is ugly.

1.) there is no need for using 'lib' without a really powerful reason. your's is none.
2.) if you like to inherit from Exporter, you better use it.
3.) $cgi->cookie(SESSION_COOKIE) is rubbish. btw.: what the made you think to establish a constant for a cookie's ... err what? value?

i'd really suggest that before you dig deeper into all that miraculous CGI stuff you take a look at mod_perl and Apache2. what you are trying to construct is at least old-fashioned.