There is a great tool to do this
HTTrack, available for Windows, Linux and Mac (instructions on download page). Works very well, however, make sure you have good bandwidth (probably an option to limit it's use) and have PLENTY of spare space on the target drive. Pprune could be hundreds of gigabytes or more.
Try doing a few tests on small sites before letting it loose on pprune. Depending upon your bandwidth, it could take somewhere between hours & weeks. It is a powerful tool, you might want to read the
manual and
What NOT to do before using it as some site administrators might interpret it's use as a Denial Of Service attack if you don't limit the bandwidth.