If you are a Veteran of the Armed Forces and you qualify for VA Guaranteed mortgage financing, then eligible Veterans are permitted to financing up to 100% of the purchase price of the home. That means no down payment.
For other HomeBuyers, Non-Veterans, the program for qualified Homebuyers with the lowest down payment requirement currently is the FHA or Federal Housing Administration. The FHA Insures mortgages made by banks and Mortgage Bankers and allows for a down payment of only 3.5%. http://portal.hud.gov/hudportal/HUD?src=/topics/buying_a_home
After FHA, Conventional financing through either FannieMae or FreddieMac allows for a minimum down payment of 5%. The Lender will need to obtain approval from a Private Mortgage Insurance company (PMI) to complete the loan approval.
The best way to have your questions about down payment and mortgage qualifications answered is to locate a local Mortgage Banker with at least 15 years experience. Mortgage professionals like myself who work for local Mortgage Bankers are Licensed as opposed to the registered status of sales people at regular banks. Thus you will receive a higher level of service which is just what a First Time HomeBuyer needs.
I hope that helps!
Trevor Curran NMLS #40140