Somebody else would have to answer that. I bet you can re-generate the public key from the private key with some openssl command, but I don't know what it is.
In the future, don't follow those instructions. Just open two terminal windows. In one open up your public key in a text editor, in the other you should ssh to the destination machine and open up the ~/.ssh/authorized_keys or authorized_keys2 file in a text editor, then just copy and paste your public key over. You can do it in one command with:
cat ~/.ssh/id_dsa.pub | ssh -l <user> <remoteserver> "cat - >>.ssh/authorized_keys2"
but I find it faster to just open up two terminals and copy/paste than to type out that monstrosity.