If you purchased in 2009 and don't want to wait until 2010 to get the refundable credit, you have the option of claiming it on your 2008 tax return. If you already filed your 2008 tax return, you can AMEND your tax return by filing form 1040X and completing Form 5405. If you haven't filed your tax return yet, and aren't closing before April 15th...you can file and extension until October 15, 2009. Once you close, you can finalize your tax return and claim the credit using Form 5405. And if you closed before April 15th, then you can just file your tax return and make sure Form 5405 is included. Either way, you should be able to get your credit in 2008.
I am not a tax professional so I would highly advise that you check with your Accountant to be certain. I had several buyers claim for 2008 and receive the "check in the mail"! Good luck!