To clarify, the $8,000 tax credit cannot be used for an FHA buyer's 3.5% downpayment. It can be used for additional downpayment, to cover closing costs and/or buy down the interest rate.
Click here for the full article from NAR's website:
http://www.realtor.org/press_room/news_releases/2009/05/tax_credit?lid=ronav0019
Click here for the actual letter from HUD with preliminary guidelines:
http://www.hud.gov/offices/adm/hudclips/letters/mortgagee/files/09-15ml.doc
$8,000 Tax Credit Basics:
http://www.realtor.org/home_buyers_and_sellers/2009_first_time_home_buyer_tax_credit
Feel free to contact me with any questions!