Koen --
Launch Microsoft Project Professional and connect to Project Server. Create
the template and then click File - Save. Select Template as the Type, name
the template, and click the Save button. If you have a project that is
already created and ready to be saved as a template, click Tools -
Enterprise Options - Import Project to Enterprise. When prompted for
Project level information, such as the template name, select Template as the
Type. Hope this helps.