Listen 80
NameVirtualHost 127.0.0.1:80
<VirtualHost 127.0.0.1:80>
  ServerName host0
  ServerAlias host0
  DocumentRoot "/host/www/"
</VirtualHost> 

Listen 81
NameVirtualHost 127.0.0.1:81
<VirtualHost 127.0.0.1:81>
  ServerName host1
  ServerAlias host1
  DocumentRoot "/host1/www/"
</VirtualHost>