I'm not entirely sure what you mean by
'you downloaded it direct from Adobe'. What exactly was it that you downloaded because Camera Raw (ACR) is a plug-in to the main Photoshop application (all versions including CS2) and NOT a standalone application in it's own right.
However, it may be that the root of your problem lies in not having the latest version of the Camera Raw plug-in installed relevant to CS2 (version 3.7) which supports your Nikon D80.
My advice to you would be to follow this path (assuming you're using a PC):
Program Files/Common Files/Adobe/Plug-Ins/CS2/File Formats and you will see a folder aptly named Camera Raw. Right click and choose Properties to check which version of the plug-in you have installed. If in fact the version number is anything earlier than v3.7 then follow this link:
http://www.adobe.com/support/downloa...jsp?ftpID=3584 - download the v3.7 plug-in replacing the earlier version in the previously mentioned folder.
When first starting CS2 the splash screen should also indicate which version of Camera Raw is installed and being used. You can also check within CS2 by going to
Help > About Plug-in > Camera Raw.
I hope this solves your problems.