Form 4868. This page:
http://www.irs.gov/pub/irs-pdf/f4868.pdf?portlet=3
Yes, send it to IRS by April 17. Remember if you owe them tax money, you need to pay by April 17 too, by sending the check with Form4868 to IRS. In other words, you can bullshiit IRS later, but must pay on time! hehehe... Good luck!