For many reasons, including converting potential earnings from capital gains to ordinary income, the potential that your IRA will not be able to benefit from depreciation or interest deductions, improper asset diversification, and high custodian costs, speak with a tax attorney of CPA/CFP before you do this.
From neutral parties, I have heard it is far better to use cash from an existing property than to use your IRA if you are going to invest in real estate right now (which is a whole different question entirely).
Be careful . . . they are not the deal that many think they are. Talk to an attorney or CPA.