>My explanations anyway were not enough understandable I think. I don't have
>a "random" NAT system in-between the two tunnel sides: the NAT system has a
>reserved (fixed) IP adress to do the mapping between this internal IP
>address and the public one, and does nothing else with these "reserved"  
>address.

	unfortunately, even with the above setup it doesn't work.  it is just
	impossible for IPsec to work with NAT, *by nature*.  for instance,
	NAT needs to rewrite packet content for FTP and other traffic,
	however IPsec ESP is designed to make it impossible to look at the
	content by encryption.

itojun