From documentation and hibernate test suite i see that it must be possible to use a composite-id key column as the column in a many-one property.
For instance something like this:
<class name="Order" table="CustomerOrder">

<composite-id name="id"
class="Order$Id">
<key-property name="customerId" length="10"/>
<key-property name="orderNumber"/>
</composite-id>

<many-to-one name="customer"
column="customerId"
insert="false"
update="false"
not-null="true"/>
</class>
<class name="Customer">

<id name="customerId"
length="10">
<generator class="assigned"/>
</id>

....
</class>
</hibernate-mapping>

I have a legacy database with no foreign key relations defined ! Can this be the reason that i get this exception? org.hibernate.MappingException: Repeated column in mapping for entity ....(should be mapped with insert="false" update="false").
For collection mappings (i found), no foreign keys relations at the database level is no problem!

Thanks in advance