Dear John, The first thing to do is to determine whether you owe the money. You can demand that the creditor or debt collection prove that you actually owe the debt. Next determine whether the statute of limitations has run its course or not. Here is a link that explains the Fair Debt and Credit Reporting Act:
Be sure to answer the law suit within the time frame, probably 20 days from the day you were served. If you don't answer, they can file a Motion for Default, and have a judgment placed against you without you ever having your day in court.
We are not attorneys, and this is not meant as legal advice. Please continue your research on your own, and contact an attorney if you are unsure of your rights or responsibilities.