I apologize for the lengthy answer, but this is good information from the National Assoc. of Home Builders:
Some people have thought first time buyer means that you have never had a mortgage, this is not correct. The $8,000 tax credit is for first time home buyers. Regardless the type of home, you cannot have had your name on the deed of a property for the past 3 years, from the date of purchase.
The law defines "first-time home buyer" as a buyer who has not owned a principal residence during the three-year period prior to the purchase. For married taxpayers, the law tests the homeownership history of both the home buyer and his/her spouse.
For example, if you have not owned a home in the past three years but your spouse has owned a principal residence, neither you nor your spouse qualifies for the first-time home buyer tax credit. However, unmarried joint purchasers may allocate the credit amount to any buyer who qualifies as a first-time buyer, such as may occur if a parent jointly purchases a home with a son or daughter. Ownership of a vacation home or rental property not used as a principal residence does not disqualify a buyer as a first-time home buyer.
Any home that will be used as a principal residence will qualify for the credit. This includes single-family detached homes, attached homes like townhouses and condominiums, manufactured homes (also known as mobile homes) and houseboats. The definition of principal residence is identical to the one used to determine whether you may qualify for the $250,000 / $500,000 capital gain tax exclusion for principal residences.