Resources for getting started with lending money

[Ben Schofield]

I have a small rental portfolio built with traditional mortgages.  I'm looking for smarter ways to fund future property acquisitions.  I have a buddy that has some money burning a hole in his pocket.  He has never done private money lending before.  What resources are out there for us to learn how to structure contracts so my buddy can act as the bank (hard money lender?) to loan money for my real estate deals and keep our friendship intact?