When in doubt, check for exceptions...
#!/usr/bin/perl -wT
use strict;
use Template;
use CGI;
my $q = CGI->new;
print $q->header("text/html");
my $template = Template->new( { INCLUDE_PATH => '/home/xxxx/yyy/zzzz'
+} )
|| die Template->error(), "\n";
my $vars = { message => 'Hello', };
$template->process( 'test.html', $vars )
|| die $template->error();
returns
Content-Type: text/html; charset=ISO-8859-1
file error - test.html: not found
Maybe you shoud just need to set your "INCLUDE_PATH" to the correct location of your test.html file?