how do I determine the ServerDN for my Exchange server

you can useADSIEdit.msc which are installed as part of the support tools and resource kit add ons for Windows 2003 Server. Install the support tools then run adsiedit.msc, expand Domain [server.domain.com], Expand DC=Domain, DC=COM, Click the OU that the server is in & find the server name on the right pane,there is a DistinguishedName field shown for the server object, that is the DN of your server. something like: CN=SERVER_NAME,OU=OU_NAME,DC=DOMAIN,DC=DOMAIN_SUFFIX (com, net, lab, test, int, local, etc.)