FYI - There appears to be an issue with Civil 3D 2008 installation that can cause the following message:
"This installation is forbidden by system policy. Contact your System Administrator. D:supportofficelockbackRegKey.msi"
The error message continues to say more, but the issue appears to possibly be related to the installation of Vault, but its not confirmed. There is a workaround that appears to install Civil 3D properly, but will not allow the installation of Vault as of yet (executing C3D.msi from the CD).
At the moment there does not seem to be an official solution to this issue, but if it happens when you attempt to install from your CD I wanted to state that you may wish to wait until a fix is discovered before uninstalling your previous version of Civil 3D unless your installation executes without issue.