As long as you still have the same plugins, you should be able to open even very old projects in the current version of SONAR, which has always been very good about backward compatibility.
Some years ago I ran across an old floppy disk full of Cakewalk 1.0 projects. The hard part was finding a floppy drive to read it from, but once I got them on disk I was able to open them in SONAR 8.5. Granted, those were all-MIDI projects; you might have issues with audio projects prior to SONAR 4. If your goal is to convert the old project to the newest cwp format, all you have to do is open it and save it, optionally under a new name.
Of course, if you no longer
have the soft synth that you'd used in the old project, then it won't matter what version of SONAR you use to open it - there'll be no information forthcoming.