These are compatable with Custom and Official firmwares 3.7X+
It never really occurred to me until now that if you want to test large amounts of icon sets, you can just stick the entire pack in your theme folder! [ms0:/psp/theme] and delete the one's you don't want via the same way to select them.
regarding this package, I honestly dont know anything about it's theme's authors or how many of them were made for 3.7X or converted to it, but it looks like a portion of them are from Sony.
the package was recompressed to save optimal space (~3mb)