For a column of type varchar I could write such a query:

public IList<Order> GetByName(string orderName)
{
 using (ISession session = NHibernateHelper.OpenSession())
 {
  return session.CreateCriteria<Order>().
   Add(Restrictions.Like("Name", string.Format("%{0}%", orderName))).
   List<Order>();
 }
}

How do I write a similar LIKE-query for a column that has type datetime?

public IList<Order> GetByDateTime(DateTime dateTime)
{
 using (ISession session = NHibernateHelper.OpenSession())
 {
  return //LIKE-query
 }
}

That is, if the method is passed the date and part-time (eg "25.03.2010 19"), then displays all orders are carried out in this period of time.