Completely transparent VPN between NATed sites

Hi,

do you think it is generally possible to run a setup such as


LAN-A ----- FW/NAT =====(internet)===== FWL/NAT ----- LAN-B
192.168.1.x                                           192.168.2.x


so that _everything_ works, including FTP, LDAP, H.323...?

I mean, practically possible :-)

I am interested in both suggestions for specific hardware and also 
especially the OpenSource solutions FreeS/WAN, KAME and builtin ipsec 
under the *BSDs.

Greetings,

René