Do the Domain Controller and Exchange need to be on two separate servers?

[TSCustomer]

I need some help understanding what I'm hearing on this video. The instructor has stated several times that it is not wise to install Exchange on a server with Active Directory. I thought Active Directory was necessary to run Exchange (?). Could the instructor mean to not run Exchange on a Domain server?

[Gosia]

In the Exchange 2003 video the instructor installs Active Directory on the same server as Exchange 2003. This setup, however, is not recommended in a production environment as Active Directory and Exchange should be on two separate servers. I am very happy you are enjoying our training video

[TSCustomer]

What has brought this up is a conversation with a local tech. He is saying that AD has to be on the server that Exchange is installed on. Are you saying that if AD was not on the server the Exchange installation would prompt you to look for a server with AD installed?

[Gosia]

Microsoft recommends installing the Domain Controller and Exchange on two separate servers. This doesn't mean that if you install them on the same server they will not work. It is just recommended to have them on different servers. You will still have Active Directory User and Computers access from Exchange server (or from any other server and even Windows XP Pro if needed).

Here is a link you might want to check out:
http://www.microsoft.com/technet/prodtechnol/exchange/Analyzer/92e23d0b-d52c-466e-b885-0e7e812efd56.mspx?mfr=true