totally fucking ridiculous!

bipp-dcd:/Users root# niutil -create / /users/markv
bipp-dcd:/Users root# niutil -create / /groups/markv
bipp-dcd:/Users root# niutil -createprop / /users/markv uid 504
bipp-dcd:/Users root# niutil -createprop / /groups/markv gid 504
bipp-dcd:/Users root# niutil -createprop / /users/markv gid 504
bipp-dcd:/Users root# niutil -createprop / /users/markv realname "Mark Vaughan"
bipp-dcd:/Users root# niutil -createprop / /users/markv shell "/bin/bash"      
bipp-dcd:/Users root# niutil -createprop / /users/markv home "/Users/markv"
bipp-dcd:/Users root# cp -R /System/Library/User\ Template/English.lproj /Users/markv
bipp-dcd:/Users root# chown -Rf markv:markv /Users/markv
bipp-dcd:/Users root# passwd markv

also

niutil -appendprop / /groups/admin users markv

niutil -list . /

niutil -read / /users/markv

niutil -read / /groups/admin