What are the rules for using other's money in a down payment?

[James Corr]

Hey BP, 

I live in a HCOL area but a fantastic appreciation market -- San Diego, CA. My wife and I both have W2s earning above six figures, between $100-150K to invest in real estate, good to great credit, and a long time table (we're in our early thirties!). With all of this said; I've been interested in MFH in San Diego, but it's expensive with a duplex running anywhere from $700-1.1. While we could probably afford this, I'd like to explore leveraging private money to fund a down payment in addition to our own funds.

Where can I get more information about taking private money - be it from a friend, family member, etc. - and using this in conjunction with our own money for an owner-occupied MFH? I.e. if I wanted to fund half of a $120K down payment and leverage private money for the other $60K, what rules exist?