Do I need a passport to travel to Acapulco, Mexico?

You'll need one is your travel dates fall after January 23, 2007. If not...then you will just need a birth certificate and ID.
(US Citizens)

Paspport to travel to Acapulco from US?... NO!!! but you will need your passport when you return to US.

Have fun !

It depends on your method of travel if by plane you need passport if trip is after Jan 23, 2007. If it is by car all you need is your id!!

I would not go there it is NOT SAFE for US Citizens! Read the Department of States warning!

It is best to have one however in reality you do not need to have one until December 31 2007. You may get hassled however not having a passport is not necessary yet. Make sure you bring your drivers license. Below are the effective dates for the Western Travel Initiative:
• December 31, 2005 - Apply the requirement to all travel (air/sea) to or from the Caribbean, Bermuda, Central and South America
• December 31, 2006 - Apply the requirement to all air and sea travel to or from Mexico and Canada.
• December 31, 2007 - Apply the requirement to all air, sea and land border crossings.

We were told we didnt need one when we just went in October. We got to Mexico City and they tripped a little. It's so much easier to have one when you are going through customs. Coming back in, was the easy part. We got an affidavit of citizenship, birthcertificate, and ID. But, you should do the passport.
They just changed the law anyhow. When we were going everyone told us after Jan 1st. you will need one.
The airlines will know for sure if you call them.
Have Fun!!