The tax credit that was scheduled to end at the end of November has been extended until June 30, 2010. You must have a signed purchase contract in place by April 30, 2010. It is for first time home buyers, meaning you have not owned a home in the last 3 years and it is up to a maximum of $8000.
They have also made it to include existing homeowners who have owned a home for the last 5 consecutive out of the last 8 years and it is to a maximum of $6500.
If you are a fist time home buyer and do not take advantage of this you are throwing away valuable dollars that can be used against your tax liability.
For more information go to Federal housing tax credit to answer all of your questions.