If the home is not a HomePath home... then the old traditional 20% down comes into play. Some lenders will require reserves, and others wont... depends on your credit score. Some lenders will count any 401K or retirment accounts you have as "reserves"
There are some "hard money" lenders out there that will court you with 10% down payments, but their rates are usually high, and most of them want you to re-sell or refinance the property as soon as you can... which you can do.. I have several investors that used "hard money" to obtain the property, and then refinanced the loan later (depending on the market value vs. the owed balance)
Sometimes, you just have to be a bit creative, but where there is a will.. there is a way.
Investment Properties are considered risky in the eyes of the Lender, so the riskier the loan, the more solid the Buyer will need to be, and the higher the down payment amount. I don't want to make it sound like it is near impossible, but just be prepared to put 20% down and have some reserve money saved up.