Getting $8,000 in tax back for buying a house?

okay if you buy a house between now to Dec of 2009. Do you automatically get $8,000 back when you do your taxes and you wont get to pay back? but does that affect only if you buy a house? what if you buy a duplex does that affect it too? And does the amount of price of the home you buy has to fall in the XXX,XXX amount require to get that $8,000 or it doesn't matter what amount of the house you buy?