If you want to use the money as a down payment and closing costs, MHDC has a program now that they will lend you the money at the time of your purchase and you repay that loan when you receive your tax credit from the IRS.
Here's some information from the IRS Website, check with your accountant for detailed info;
Special election to treat purchase as made in prior year.
In the case of a purchase of a principal residence after December 31, 2008, and before July 1, 2009, a taxpayer may elect to treat such purchase as made on December 31, 2008.
For more detailed information on qualifying for and claiming the first-time homebuyer credit, refer to additional topics on this subject on the IRS Website at http://www.irs.gov.