Are the files in the SuperPaint file format or Pict or....?
Unfortunately, the PICT files saved from SuperPaint will only open in photoshop cs4 and older on the mac side.
The SuperPaint file format is a form of Pict files and can also be opened in photoshop cs4 and older.
Photoshop cs5 and newer only have minimal support for PICT files as do newer mac os's Preview Application.
They don't support vector data and such anymore in PICT files.
Newer versions of Lemke GraphicConverter won't open the SuperPaint file format.
What operating system do you have access to now?
My suggestion would be to see if you can fix your mac mini, get another mac g4 or use an emulator like SheepShaver.
Then In SuperPaint you can use File>Export>Entire document to TIFF and open that in photoshop cc or most any other image editing application.