Uninstall PPM-Sisyphusion, or use --force to allow files to be overwritten

Either way should work.
PPM won't overwrite a file of the same name - even if it's identical (as will always be the case with my ppm installations).
It looks like Class-Inspector is going to install its own files plus the ones that PPM-Sisyphusion did, so I'd probably run:

ppm uninstall http://www.sisyphusion.tk/ppm/PPM-Sisyphusion.ppd
and then the other commands:
ppm install http://www.sisyphusion.tk/ppm/Class-Inspector.ppd
ppm install http://www.sisyphusion.tk/ppm/Capture-Tiny.ppd
ppm install http://www.sisyphusion.tk/ppm/File-ShareDir.ppd
ppm install http://www.sisyphusion.tk/ppm/Alien-SDL.ppd
ppm install http://www.sisyphusion.tk/ppm/SDL.ppd
[download]

I'll be off-line now for a few hours - but I'll pick up again in the morning when I wake up.
Hopefully it'll be plain sailing from here, anyway.

Cheers,
Rob