There is no link via email addresses between Steam and Battlenet. If you wish to start fresh on Steam, then simply create or use an existing account there. When D2 goes live on Steam, download the New Light version for free. Then go to bungie.net and log out of any logged in account. Then click Join Up, then select Steam and then enter your Steam credentials. Using this method gives you an entirely new and separate profile from the Bungie profile you created with your Battlenet login. This is assuming you want absolutely nothing to carry over, no special emblems, no game play history, nothing. If you do want some stuff to carry over then you need to log in to bungie.net with your Battlenet account, then go to Account Settings, then Accounts and Linking and then add your Steam account to that Bungie profile while logged in under your Battlenet credentials.