The following is from Autodesk, any errors or ommisions are theirs.
Solution
To uninstall AutoCAD® Civil 3D® 2008 and remove any remnants of this product from the system, follow these steps:
Important! Back up any existing custom Civil 3D 2008 files before you implement the following procedures.
To uninstall AutoCAD Civil 3D 2008
Click Start menu (Windows) > Settings > Control Panel.
In Control Panel, double-click Add or Remove Programs.
In the Add or Remove Programs dialog box, select the AutoCAD Civil 3D 2008 product and click Add/Remove. (For Windows 2000, click Change/Remove; for Windows XP Professional, click Remove).
Click Yes when prompted to confirm that you want to completely remove the application and all of its components.
If you are prompted to remove shared files, click No to All, and then click Yes when prompted for confirmation to proceed.
After the uninstall procedure has completed, click OK.
Restart the computer.
To remove any remaining AutoCAD Civil 3D 2008 files
Using Windows Explorer, delete the following Civil 3D 2008 installation folder:
C:\Program Files\AutoCAD Civil 3D 2008
Note: If your operating system is configured to store the Program Files folder on a drive other than C, adjust the file path accordingly.
Delete the C:\Documents and Settings\All Users\Application Data\Autodesk\C3D 2008 folder.
Delete the following folders:
C:\Documents and Settings\<user>\Application Data\Autodesk\C3D 2008
C:\Documents and Settings\<user>\Local Settings\Application Data\Autodesk\C3D 2008
Note: You need to delete these folders for each Windows user account.
To remove any Civil 3D 2008 entries that remain in the Windows registry
Warning! Problems caused by improperly editing the Windows registry could render your computer operating system unusable. Microsoft provides a wealth of critical information that you need to know about the registry in the Microsoft Knowledge Base at
http://support.microsoft.com/support.
Use the Microsoft® Registry Editor only at your own risk and only after backing up the registry as well as the system.dat and user.dat files as outlined for your operating system in the Microsoft Knowledge Base and in the related solution, TS66513. Additional information about the registry is also contained in the Help topics in the Microsoft Registry Editor.
Log on to the computer as a member of the Local Administrators group.
Click Start menu (Windows) > Run.
In the Run dialog box, enter regedit and click OK.
In the Registry Editor, locate the following subkeys and delete them:
HKEY_CURRENT_USER\Software\Autodesk\AutoCAD\R17.1\ACAD-6000:409
HKEY_LOCAL_MACHINE\Software\Autodesk\AutoCAD\R17.1\ACAD-6000:409
Close the Registry Editor.
Restart the computer.
AutoCAD Civil 3D 2008 has now been completely removed from your computer.
Reinstalling AutoCAD Civil 3D 2008
Before you reinstall Civil 3D 2008, delete the contents of your Windows Temp folder. If you are working with Windows 95, Windows 98, or Windows Me, your Windows Temp folder will typically be found at C:\Windows\Temp. If you are working with Windows NT 4.0, Windows 2000, or Windows XP, your Windows Temp folder will typically be found at C:\Documents and Settings\<user>\Local Settings\Temp.
You should also close and temporarily disable any anti-virus software that may be running on the system. You can use the End Task feature to close the anti-virus software. Disabling the software from the system tray may not be sufficient. Anti-virus software may be used to block certain activities (for example, access to the registry, adding, removing, or updating DLL files, and so on) that are seen as suspicious, even though these activities are common when installing or removing programs. Several anti-virus programs can be disabled by right-clicking their taskbar icon and clicking Disable on the context menu. For more information about disabling your anti-virus software, refer to the software vendor.
To verify that an anti-virus program is not running in the background as a TSR (Terminate and Stay Resident Program)
In Window 95, Windows 98, and Windows Me:
Press CTRL+ALT+DELETE.
In the Close Programs window, select the anti-virus program and click End Task.
In Windows NT, Windows 2000, and Windows XP:
Press CTRL+ALT+DELETE.
Click Task Manager.
In Task Manager, click the Processes tab.
Select the process for the anti-virus program, and then click End Process.
Now, you can reinstall AutoCAD Civil 3D 2008 on the computer.
It isn't always as straight forard as this; as I just fought through this and some whacky 64bit issues and License Server challenges just yesterday afternoon. In the end I prevailed, and today I get to share that learning experience with you.
