how can I add an event receiver to the style library ? (can't find any templateid)
On Elements.xml, use ListUrl instead of ListTemplateId
A style library uses the document library template (101), so that is the ID you use to create an event receiver.
The following link provides a detailed list of template ID's for registration: http://techtrainingnotes.blogspot.com/2008/01/sharepoint-registrationid-list-template.html