T.G.
Riley's response is great. I work for a lender. The debts will appear on your credit report for 7 years from the most recent date of last activity (last payment, etc). As she said if the debts are old it will probably work against your credit if you start paying on them now. Even if you pay in full, now you would have an account that has a 2009 activity date vs an account that has a 2006 or 2005 date. Your credit score will actually go down due to the more recent dates. Anything over 1 year old will just re-set the clock and then instead of having old collection accounts you will have newer collection accounts (even if they are paid). The letter you received threatening to take you to court is one way creditors can get the dates re-set. You mentioned $21k in debt. If the company that sent you the letter is owed a majority of that $21k they may take the time and expense to file a judgement against you. However most collection agencies are not going to go through the time and expense of filing a judgement. I would be really careful about filing a BK just due to some old collection accounts. You probably should talk to an attorney.
I think the items you can request from the collections company are:
1. copies of any papers that show I agreed to pay what you say I owe;
2. Full payment history
3. Explain and show me how you calculated what you say I owe;
4. Prove the Statute of Limitations has not expired on this alleged debt.
Regarding number 4, I have heard (can't say for sure, but...) that after 3 or 4 years the collection agencies can't keep contacting you regarding the debts, so you may just be getting close to that cut off time and they are making one last attempt to see if they can get $$$ from you. You must make the request in writing and the agency has 90 days to respond.
Going forward, I would make sure that all your current bills are paid on time. Check with your bank or credit union to see if they have someone that could work with you on a budget.