It's a little confusing on the 6.6 ReadMe -
Compatibility
The Camera Raw 6.6 plug-in is not compatible with versions of Photoshop earlier than Photoshop CS5 or versions of Photoshop Elements earlier than Photoshop Elements 8 for Windows and Photoshop Elements 8 for Mac.
The latest version of the Camera Raw plug-in available for Photoshop Elements 8.0 (Windows, Mac) is Camera Raw 6.2.
This is from the 6.2 ReadMe -
Photoshop Elements:
Windows®:
NOTE: You must follow all of the new instructions in order to successfully install the Camera Raw Plug-in for Photoshop Elements.
1. Exit Photoshop Elements.
2. Open the download file and double-click CameraProfiles.exe and follow the on-screen instructions.
3. Double-click Local Disk (C
.
4. Navigate to the following location:
a. Program Files\Common Files\Adobe\Plug-ins\Elements 8\File Formats
5. Move the existing Camera Raw.8bi plug-in to another location (for example, a new folder on your desktop). Ensure you keep this version in case you need to revert back.
6. Copy the Camera Raw plug-in, Camera Raw.8bi, from the download into the same folder as Step 4.
7. Launch Photoshop Elements
Did you follow the directions?