Here is official information on the Homebuyer Tax Credit extension.
First Time Homebuyer Credit general information on IRS.gov
http://www.irs.gov/newsroom/article/0,,id=204671,00.html
First Time Homebuyer Credit Questions and Answers on IRS.gov (This page includes Q&A broken out by basic questions, 2008 purchases, 2009 purchases and scenarios.) http://www.irs.gov/newsroom/article/0,,id=187935,00.html
