Manual update instructions for Photoshop CS2 and Photoshop CS3 Windows:
Download the updated file ps_security_update.zip 
Exit Photoshop. 
In Windows Explorer, navigate to the following location(s): 
For CS3: C:\Program Files\Adobe\Adobe Photoshop CS3\Plug-Ins\File Formats; 
For CS2: BMP & TARGA: C:\Program Files\Adobe\Adobe Photoshop CS2\Plug-Ins\File Formats; PNG: C:\Program Files\Adobe\Adobe Photoshop CS2\Plug-Ins\Adobe Photoshop Only\File Formats 
Move the existing plug-ins to another location (for example, a new folder on your desktop). Ensure you keep these original versions in case you need to revert back. 
Copy the BMP, PNG, and Targa plug-ins from the download into the same folder as in Step 3. 
Launch Photoshop CS2 or Photoshop CS3.