For those setting up a windows 2008 certificate services server, pay attention when using templates:
The catch here is that the webenrollment part of the Windows 2008 AD CS only can handle v1 or v2 templates. So if you choose "Windows 2008" template when duplicating your template, you will only be able to use it for auto-enrollment purposes or enrollment by the mmc. It will not appear on the certsrv website.
When you duplicate a template in orde to change settings like the validity period, the template becomes a version 2 (Windows 2003 ) or a version 3 (Windows 2008 ) certificate. The out of the box provided certificates are version 1 certificates.