As per the IRS rules, "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." Thus, it would seem that you would qualify for the First Time Home Buyer Tax Credit.
The IRS would disqualify you from qualifying for First Time Home Owners Tax Credit if any of the following situation apply to you:
1. Your income exceeds the phase-out range. This means joint filers with Modified Adjusted Gross Income (MAGI) of $170,000 and above and other taxpayers with MAGI of $95,000 and above.
2. You buy your home from a close relative. This includes your spouse, parent, grandparent, child or grandchild.
3. You do not use the home as your principal residence.
4. You sell your home before the end of the year.
5. You are a nonresident alien.
6. You are, or were, eligible to claim the District of Columbia first-time homebuyer credit for any taxable year. (This does not apply for a home purchased in 2009.)
7. Your home financing comes from tax-exempt mortgage revenue bonds. (This does not apply for a home purchased in 2009.)
8. You owned a principal residence at any time during the three years prior to the date of purchase of your new home. For example, if you bought a home on July 1, 2008, you cannot take the credit for that home if you owned, or had an ownership interest in, another principal residence at any time from July 2, 2005, through July 1, 2008.