They cannot stop you from claiming social security. But they can and will levy upon it. Here is a good explanation of the alternative methods they use and the exemptions available to you.
Did you file returns for the years at issue in the '90s? If not, the statute of limitations has not started to un. If you have, however, the IRS only has ten years to collect from you. This period could have been tolled while you were negotiating an Offer in Compromise with them.
You might consult a competent local attorney who has experience in obtaining bankruptcy discharges on old IRS income tax debts. Even if you have to use Chapter 13 it will stop the interest accrual and limit the period from ten to five years from acceptance of plan.