Dave,
The earnings requirement for IRA contributions includes both W-2 wages, and also self-employment income - however, you can only count NET self-employment income. So if all of your deductions are going against your self-employment income, such that you show zero net income from the business, you will be unable to make a deductible IRA contribution.

You can see more information about the earnings requirement at http://www.fairmark.com/rothira/iracomp.htm.

Also, it's worth noting that if you have enough deductions to reduce your taxable income to $0, it would be better for you to make a Roth IRA contribution, not a deductible IRA contribution. After all, if your deductions have already reduced your income to $0, there's no value for another (IRA) deductions from here.

I hope that helps a little!
- Michael