You should not really have any problems. One workstation I use I have office 2000, and use Office 2007 as my mail client and I have no problems at all with the set up. You will want to make sure you get the <a href=”http://www.microsoft.com/downloads/details.aspx?FamilyId=941B3470-3AE9-4AEE-8F43-C6BB74CD1466&displaylang=en”>Office 2007 compatibility pack</a> so that your older version of office will be able to read the new formats of the rest of the Office 2007 suite.
You cannot use Word as the e-mail editor. Office and Outlook must be the same version for this option.