Tax liens are severely detrimental to your credit report. They can remain on your credit report for 7 years from the date the amount owed was paid, NOT the date of filing. If the lien remains to be unpaid, it can stay on your credit report much longer.
If you have a tax lien on your credit report, the first thing you want to do is be sure it's accurate. You'd be surprised at the number of inaccurate listings on credit reports.
If it's not accurate, you'll want to send off a letter (there are professional firms that can help make this process easier on you) asking the IRS to verify the debt. If it's unverifiable, then it must be removed. If the debt is validated, then you must pay the debt. There are tax negotiators that can help you lower the debt for a fee.