I've been messing around with the older versions of NeXTSTEP and one of the interesting (and useful!) things I found is that you can mount a NeXTSTEP dd image from an OD/HDD under linux...
mount -t ufs -o loop,ro,ufstype=nextstep image dir
That's a whole lot better than tar/cpio/etc. IMHO.
Yes! Works for floppy images and CDROMs, also.
If only we could write back to them..