Loans and gifts can help with your down payment but you can not use this strategy for all loan programs. The most popular program for this tactic is the Federal Housing Administration or FHA. FHA allows 100% gift funds for your down payment. The gift can be from any relative or can be collected through new innovative programs, like the Bridal Registry where couples receive money into an account that can be used for the down payment.
Most lenders will require that a "Gift Letter" or "Gift Form" is filled out. It is a simple letter stating who is giving you the money, what their relationship to you is, and where they are getting the money from. The person giving you the gift may also need to show a bank statement or some other documentation of where the money is coming from, and they will need to sign a letter stating that it is a gift and not a loan.
Most loan programs will allow for a certain amount of money to come in the form of a gift from a family member. The amount that is allowed will depend on not only the lender and the home loan program you choose but usually how much money you are putting down also. Talk with your mortgage professional to see how much will be allowed for you to recieve from a family member and what the underwriting guidelines are.
Not all down payment gifts come in the form of cash. If you are buying the property from a family member you may also be gifted equity in the property.
Also, ask your mortgage professional whether there are programs offered by state agencies that provide downpayment grants/loans for first-time home buyers. Many states have such programs.