The OS needs to be running to decompress files on the fly. When a game like Turrican runs it kills the OS, so any files that weren't decompressed before the game finishes exectuting and switches the OS off won't decompress once the game is running because it can no longer address PowerPacker from within the game.
Even if the game itself allows for OS operation and can tolerate having to unpack mapfiles etc on an as and when basis, if this is the same thing they used in the later Amiga magazine coverdisks I question how much it'd be worth anyway - I seem to recall powerpacker being exceptionally CPU intensive.
