You need Adobe Camera Raw (ACR). Go to the download page and download the last vesion for CS3, believe it was 4.6.
Be aware that each version of Photoshop has its own series of ACR.
So if you have a latter model camera it might not work with an older ACR. To check look here http://kb2.adobe.com/cps/407/kb407111.html
The free DNG-Converter should be able to handle the same images as the latest version of Camera Raw.
Why do you make no mention of what camera the images originated from or the file extension?