If you are being audited and you have not done your taxes since 2005, you really need to take all your information to a tax attorney or CPA that can discuss your issues with the IRS directly on your behalf.

Generally speaking, you can only file taxes for three years (subject to penalties and interest - tax is still due on April 15).

Listen to me very carefully. There are statutes of limitations that stipulate how long the IRS can pursue collections and exceptions to those statutes as well. Only a qualified tax attorney, CPA, or enrolled agent can look at your situation and make sure you are adequately represented and don't do anything that would cause the statutes to essentially start over. Instead of installing TurboTax, call an accountant/lawyer first thing Monday morning, that's my advice.