select * from tabela
where
   (dataBegin between '2011/04/13 13:00:00' and '2011/04/13 14:00:00'
   or ((dateadd(minute,tempo, dataBegin) >= '2011/04/13 13:00:00') and
      (dateadd(minute,tempo, dataBegin) <= '2011/04/12 12:00:00') )

ICriteria query = session.CreateCriteria(typeof(tabela))
                   .Add(Expression.Between("data", dataBegin, datafim))
                   .Add(Expression.Or(
                        (Expression.Sql("dateadd(minute,duracao, dtInicio) >= ? ", dataBegin, NHibernateUtil.String))
                        (Expression.Sql("dateadd(minute,duracao, dtInicio) <= ? ", dataEnd, NHibernateUtil.String))
                        ))
IList<tabela> listevento = query.List<tabela>();

select * from tabela
where
   (dataBeginbetween '2011/04/13 13:00:00' and '2011/04/13 14:00:00'
   and ((dateadd(minute,tempo, dataBegin) >= '2011/04/13 13:00:00') OR
      (dateadd(minute,tempo, dataBegin) <= '2011/04/12 12:00:00') )

ICriteria query = session.CreateCriteria(typeof(tabela))

     .Add(Expression.Between("data", datainicio, datafim))

     .Add(Expression.Or(
          (Expression.Between("data", datainicio, datafim)),
           Expression.Conjunction()
                      .Add(Expression.Sql("dateadd(minute,duracao, data) >= ? ", datainicio, NHibernateUtil.String))
                      .Add(Expression.Sql("dateadd(minute,duracao, data) <= ? ", datafim, NHibernateUtil.String))
          ))

IList<tabela> retorno = query.List<tabela>();