If I remember correctly a SITE Connector is for sites with-in the same org and will not work going across orgs.
If all you want to do is send messages between the two systems then use X.400 over TCPIP or use SMTP.
If you want trade calendar information or public folder data, then you will need the Interorg replication utility.
If you want to synchronize your Globabl Address List with that of the other ORGs GAL then you will also need to use the Interorg Synchronization Utility.
Using the Interorg tools does require having a bridge for messaging already in place - again this would be either with X.400 or SMTP.
(Please anyone - if I'm wrong then correct me. )Thanks
Rick