I don't think CS3 Raw supports your camera...here's the official list
http://www.adobe.com/special/photoshop/camera_raw/Camera_Raw_4.6_ReadMe.pdf
Unfortunately Adobe only include the latest updates in their newest software - you may need to update to CS4/CS5 - check out the official Adobe info
Simon
Do a search on Adobe website for the latest version of DNG convertor . You use it convert your raw to adobe raw .That should solve your problems .
If you've downloaded version 5.7 of the DNG converter, files converted to this standard may not be readable with CS3
At the bottom of the start page is the preferences option. Click on this and select compatibility. I think you need to use version 4.1 for CS3. Try this on a few file and see if it works OK.
It may also be worthwhile checking what the last version of ACR is compatible with CS3 and make sure you have that installed.