you can contact Servarica to get a ready to use OS templates (compatible with Xenica).
or you can learn more here :

Create LinuxTemplates :
http://wiki.xenmodule.com/doku.php?id=linux_template_creation

Create Windows Templates :
http://wiki.xenmodule.com/doku.php?id=cretate_windowstemplate_new


to get more info, please visit : 
http://wiki.xenmodule.com/


