You can actually file for the tax credit immeditly after settlement. I did and it will take 8-12 weeks to get the check.

Home buyer
Kim, MD

If all goes well, Buyers can tap tax credit for down payment
First-time homebuyers will soon be able to access their $8,000 federal tax credit when closing on a home through a short-term bridge loan that will cover their down payment on FHA-backed loans.
The Federal Housing Administration will soon publish a policy that will allow FHA-approved lenders, HUD-approved nonprofits, and state and local housing finance agencies to "monetize" the tax credit through short-term bridge loans, Secretary of Housing Shaun Donovan said Tuesday.

Again, there a motion going on to get this pass, so keep you eyes opened.

The first time buyer tax credit is not received until after a person buys that first home and claims the credit on their tax return. At the time you qualify for your mortgage and close on your purchase, you do not yet have the tax credit and therefore cannot count it as a down payment. Contingent assets are not acceptable to sellers or to underwriters. Also, although this tax credit is a terrific incentive for first time buyers, it's part of your annual federal tax filing, not a separate check from the government, so any net amount received depends on your overall tax situation.

If you're concerned about funds for your down payment, then use a government loan program. The first time buyer tax credit is for the purchase of a primary residence, and that's exactly what government loan programs such as FHA-insured mortgages are also for. With a government loan, it's feasible to buy your own home with a down payment of zero to 3.5%, depending on the program. To discuss your options, feel free to contact me: James Wheeler, 813-600-3428.

There is a lot of confusion about the credit. Go to the hud web site and read the details. http://www.hud.gov.
If you sit down with a mortgage professional you might be able to get an idea of how much you qualify for and the amount of money you will need for down payment and closing costs. The rates are low right now.

The way to use it for a down payment is to start reducing the amount of money that is with hold from your income or that you pay for your quarterly payments, if you are self employed. The other possibility would be to find a family member or friend who would be willing to lend you the money for a while.
I red in one of the financial websites that the $ 8000 can be claimed in the 2008 tax filing. If this is true it might make sense to buy very quickly before the April 15 filing or ask for an extension till October 2009.

The only thing I can add is that it is money that you do not have (yet) and cannot be counted towards a downpayment. Imagine the complications if someone were to and then moved or sold within the year before they even filed their 2009 taxes and received the funds.

It is a tax credit for 1st time buyers for their primary residence. Up to $8,000 that does not have to be paid back as long as you own the home for 3 years. It cannot be used as a down payment. You 'receive' the money as a credit on your tax return. If you purchase this year, you could file for the credit in 2010 on your return.