joshgolob,

Peer-to-peer lending practices are new and evolving rapidly, so you will want to check with the lender you are considering borrowing from to confirm just how they will or will not report your activities to credit reporting agencies.

The largest, Prosper.com, current claims at http://www.prosper.com/help/topics/start-faq.aspx that they report all activity. I could not find clarification on exactly what format this reporting takes.

Do keep in mind that most lenders are quite strict about not allowing borrowed funds for the down payment. They will often demand an accounting of where that money came from in order to enforce prohibitions against this practice.