It will have no impact on the credit, but if you do not owe enough taxes, you won't get the full credit. Since I'm single and not a homeowner (aka lots of deductions) the AMT didn't affect me and I got the full credit. However, since I only have to write a small check to the feds every year, I had to change my W2 so I would have had to pay a lot more in taxes (approximately $2100 more

) Then the full credit comes along and knocks that down back.
Just remember to change your W2 at the end of the year.