Your credits aren't saved on your machine, so you can't. Your hash, that lets the others recognize you is saved in cryptkey.dat, and the credits of the other users you know are stored in clients.met iirc (everything written from my mind). But why do you want to save these files for installing aMule? Your home isn't touched, or do you reinstall your system, in that case it's never a bad idea to backup your complete home without thinking about single files.
