We want to look into the possibility in changing our domain name for our organization because right now the domain name and dns name are using the same name. Are there any precautionary steps we need to take with our Exchange 2003 Enterprise Clusters before we do such a change? What might break, etc?...

You can rename you AD domain name. But dont take lighty on this, its very easy to do wrong and then your entire AD is in a non working state. To rename AD domain name you need a tool, Domain Rename Fixup. http://www.microsoft.com/downloads/details.aspx?familyid=24b47d4a-c4b9-4031-b491-29839148a28c&displaylang=en read the docuemntation very carefully before proceeding