How do you get creditor to correct wrong information on your credit report?

This hapenned to me in the past. I was registered with experian, I had no defaults on my credit report, however a loan company told me that I had a default on my credit report I then told them that I had checked my experian credit report and it was clean but they told me it was equifax where the bad report was logged on. I checked it and it was for a credit card I had never even heard of. Equifax investigated it and found out in a couple of days that I had nothing to do with it. This was in 2007 about when it was removed. its now 2011 I also found out recently that you can actually sue companies that put false information on your credit report.