[SMARTY] ??Cannot Instantiate None Existent Class???

I'm still working on the fact that I can not run Smarty on my server.  I 
think I'm getting closer to being able to use it though...

I've been working with the code in the 'extended' setup section of 
smarty.php.net

Could someone please tell me what this error means and how can I fix it?

Fatal error: Cannot instantiate non-existent class: smarty_guestbook in 
/usr/local/plesk/apache/vhosts/myserver.com/httpdocs/smarty/index.php on 
line 16

Thanks,
Roger