I need to revise my answer, but it may be a bit too late.
You are now allowed to use your potential tax credit for being a first time buyer as part of your down payment and/or closing costs. However, you cannot use in inplace of the required amount you need, but in addition to it. Also, in order to do this, you must go through a non profit organization (NPO) to administer it. And it's actually a loan....interest free, but still a loan. The NPO may charge you an administration fee and other misc fees but they would be rather inexpensive. If the NPO loans you $8000, but you actually only get $6000 from the gov't, you still have to pay back to the NPO, the full $8000.
Besides all this, I'm not aware of any NPO's in the Phoenix area administering this program.
Buyer's Agent Realtor