Having just upgraded a server to Windows Server 2008 with Microsoft Exchange 2007 I came accross a frustrating issue.
If IPv6 has been disabled on your network interface prior to installation of Exchange 2007 then Exchange will fail to install the Hub Transport Server role with the following error,
Service 'MSExchangeTransport' failed to reach status 'Running' on this server.
Other Exchange services will fail to start if IPv6 has been unticked in your network adapters configuration settings. I routinely disable IPv6 if it is not needed on the network, but it seems Exchange has been written to utilize the new protocol and requires it to function.