Do you NEED a passport to travel from Canada to the USA (by airplane)?

My parents want to come visit me soon. I live in the US and they are Canadian residents. They will probably fly out of New Hampshire or Vermont. Neither of them have a passport. Do you need a passport to be able to fly or can you use other identification, like a birth certificate or driver's license or both? They are working on getting a passport but probably wouldn't have it in time (they want to come visit in two weeks). Thanks in advance for any help!
We just called the airports and because they will be flying from the US, it is considered a domestic flight so they only need their driver's license. Thanks for your answers though!

They do need a passport. For a while the birth certificate was good for Canada / Mexico...but now a passport is required.

You don't need a passport until January, 2007

http://www.ppt.gc.ca/index.aspx?lang=e

i am not sure but i think if you have a birth certificate and drivers license you can. but to make sure call the immigration office.

To fly in, yes. To drive in, not until January.

Your parents can still fly without a passport but only until January 8, 2007. They will need to bring a certified copy of their birth certificate - not the little laminated ones that many Canadians carry in their wallets and a valid photo ID.