Is there a minimum taxable income limit for ROTH IRA?

I am a foreigner with J1 who had a taxable income of $42,000 for 2007 (I just found out it is taxable since I changed to J1 from F1 student visa, which make me ineligible for the tax treaty). My wife, a H1 visa holder, had a taxable income of $2000 in 2007 (she had a non-taxable fellowship when she was a F1 visa holder in most time of 2007). My question here is: Can each of us contributes $4000 separately for 2007 ROTH IRAs ?