Photoshop CS3 uses version 4.x of the Camera Raw plug-in, which opens raw files.
What camera is it? Is it newer than your version of Photoshop? Adobe may not have known about the raw format for your camera back then, and they stop updating the Camera Raw plug-in when they do the next major release (which would have been CS4 in your case)
The good news is that prior to that release, they do make updates to the Camera Raw plug-in. You can find the list of supported cameras (along with a link to download the latest Camera Raw update) here:
Look in the Camera Raw 4.6 ReadMe file for the complete list of supported cameras.
If it turns out your camera is too new to be supported by Photoshop CS3, there's still hope - Adobe provides a free converter called the "DNG Converter" that you can use to convert your raw files to a format your Camera Raw 4.x plug-in can open. It's not as convenient as just opening files into Photoshop, but it is free.
Super WOW! Thanks so much for that great information. Although, the Camera
Raw plug in didn't work I guess I will get to try the DNG Converter.