site connection

I would like to know, 1. how would or should I connect to different site together ( finsys.com and edgar.com) we are both the same co. We were bought out by edgar and would like to connect both exchange 5.5 mail together. What would I be able to seeif this could be done, example, calenders, public folders, address book, and etc. what benefits could I get from this? how would I best go about this? Should I use X400 or site connector? I know both should be trusted. I am most concerned about whateach other would see.