|As far as I know, you haven't been able to open SuperCalc files in Excel since Excel 95. If you have Excel 95 lying around, you could open it, save it as an Excel file and then open it in a newer version of Excel.|
If you still have a copy of SuperCalc (which I doubt) you could open them and then save them in a format that Excel can read (e.g., text, CSV, SYLK, etc).
If it's a really important file, you might want to try a 3rd party conversion company, which you could find via Google.
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