My company has acquired another company, and we would like them to use a different domain name as well as our own. What do I need to do on the Exchange 2007 server to get that setup? They will need to be able to send and receive using that domain name.

Configured Hub Transport Server with accepted domain, create an email policy for that group of users (i typically use custom attributes) that will assign their primary smtp address giving them the required email addresses they need with the domain. Change the mx records for the acquired company to point to your org. SF - MCITP:EMA, MCTS: Exchange 2010, Exchange 2007, MOSS 2007, OCS 2007 -- http://www.scottfeltmann.com