Hi Ladynred-
I recently joined an 'Identity' protection and credit profile notification service agency ( not sure if it's kosher to provide the name and link), and they have a section called 'dispute' on which they give you both addresses for Equifax and Trans-Union, but for not for Experian. This is what they have on that section:
Equifax
P.O. Box 740256
Atlanta, GA 30374-0256
TransUnion
P.O. Box 2000
Chester, PA 19022-2000
Experian
Disputes are not accepted by mail or telephone, but you may file a dispute online.