Server Configuration

I am attempting to integrate a single machine running Ubuntu 10.04 LTS as a file server into my current network configuration. My configuration currently has one server running Windows Server 2008 R2 and one server running Windows server 2008 with Microsoft Exchange 2007. There are 70 desktops and 10 laptops all running Windows XP Pro which connect to these two servers. I need all of these machines to be able to connect to my new server as well. The Exchange server is solely an e-mail server. Currently all other networking tasks are handled by the Windows 2008 R2 server. I do not want to give up Ubuntu, as I love the features the OS has, but I cannot get this new machine to see my Domain Controller (Windows 2008 RS,) and if I can't even see the domain controller I have no idea how to get it onto my domain. Any ideas?