Deploying Exchange 2007 Update Rollups, don't forget you need internet access!
To update your Exchange 2007 Servers, you need to deploy the so-called update rollups, which contain a number of fixes and modifications to make sure your Exchange Servers are always up-to-date. You can find information about the latest update rollup that is available for your Exchange deployment here: http://support.microsoft.com/?kbid=937052
However, keep in mind, that when deploying an update, make sure your Exchange Server can access the internet after rebooting it to complete the installation of the update rollup.
The reason is that Exchange will try to connect to the following Microsoft Web Site: http://crl.microsoft.com/pki/crl/products/CSPCA.crl
to download the latest Certificate Revocation List. If it fails to connect to the website, some services will fail to start, like the Microsoft Exchange Service host, which provides a host for several other Microsoft Exchange services. More information is available here: http://support.microsoft.com/kb/944752