Buying no title what should i do??

I want to buy a motocycle from a private seller. He does not have the title and is also not the last registered owner. He told me all I would have to do is put a lien on the bike and that I would either have to wait 30 days for lien to clear, or the last reg owner would pay the lien amount to me.
Anyways I was just wondering if this is true and legal. I go check it out tomarrow...