Adobe cut RAW support at pre-D600 for all versions of CS from 5.5 back. Adobe Camera Raw 7.3 will only work with PS CS6 (and on, until they cut it in the future)
It's a pretty lame move and I'd encourage you to drop Adobe a line to register your disappointment - how ever futile that might be.
You can use ViewNX to Export your RAW file to PS CS4
or use the Adobe DNG convertor to make DNG copies of your D600 RAW files that will open in CS4. Lightroom 4 will also export to a tiff in CS4 and there are a couple of other work arounds. BUT D600 RAW in PS CS4 is not an option.