Host two domains on Exch2000?

Hello, we are currently running two different Exchange 5.5 servers at our two different companies. We are planning an upgrade to Win2K and Exchange 2000 and connecting both locations with a T1. My question is can I receive and send for both domains on one Exchange 2000 server? I’ve seen receiving for more than one domain in Exchange 5.5, but it seemed to me that when the recipient replied, it always went out as from the primary domain. We would like to make it seem separate, so that when a user@sistercompany.com replies it doesn’t go out as user@parentcompany.com. Thanks.