You may be able to delay the 2005 tax return deadline until April 17th, 2007 by filing form 4868 by October 16th. (You cannot extend the 2004 tax return deadline.) You must write “Hurricane Katrina” at the top in red and an estimate of how much you estimate you still owe the IRS. This is not an extension of time to pay, though, so any taxes not paid by October 16th will begin to accrue interest and penalties unless you have mad a payment arrangement with the IRS.
For more information on this, you can read their news release.
For more assistance with filing a Katrina (or Rita or Wilma) affected return, see this page on the IRS website.
If you still have questions, you can contact the IRS or ask a question on our User Forums.
I hope this helps!