Resetting PowerBook to "as new"

I got my powerbook free from a friend who had spilt wine on it. I took it apart and put it back together and it worked. I managed to delete his old admin account and reset the mac so that it thought it was brand new by holding something at boot up, and then entering a couple of lines into the command prompt.

I'm selling the mac on ebay now to raise some cash, and I've said that i'll reset it in the same way for the next user. Now that I've come to look up the same article on the internet, I can't find it.

Does anyone know how to do this? I cant for the life of me find that article.

Cheers