If you own your home - you do not qualify for the first time home buyer's credit.
See instructions for the form 5405 - http://www.irs.gov/pub/irs-pdf/f5405.pdf
In general, you can claim the credit if you are a first-time homebuyer.
Your main home is the one you live in most of the time. It can be a house, houseboat, housetrailer, cooperative apartment, condominium, or other type of residence.
You are considered a first-time homebuyer if:
You (and your spouse if married) did not own any other main home during the 3-year period ending on the date of purchase.
If a small mobile home is your main home and you owned it during the 3-year period ending on the date of purchase - you would not qualify fro the credit.
If you sold it at least three years before the purchase - you do qualify.
Sorry if you expected a different answer.
Let me know if you need any help.