Recently I had a question regarding a Cannon 5D Mark 2 camera and Photoshop CS3. The Raw files from this camera would not open in CS3. Adobe stopped supporting CS3 after the launch of CS4 and there were no more updates available for the Camera Raw feature. However, Adobe does offer a DNG converter which is a great work around for this. It will take your new files and convert them to DNG which can be opened by earlier versions of Photoshop, namely CS3.
For a listing of all (at date) 275 cameras supported click here.