Uh nope...
"Visas and Travel Documents
Getting Into Mexico
Current Requirements for Getting Into Mexico: The Government of Mexico requires all U.S. citizens to present proof of citizenship and photo identification for entry into Mexico. However, U.S. citizens have encountered difficulty in boarding flights in Mexico without a passport. The U.S. Embassy recommends traveling with a valid U.S. passport to avoid delays or misunderstandings. However, U.S. citizenship documents such as a certified copy (not a simple photocopy) of a U.S. birth certificate, a Naturalization Certificate, a Consular Report of Birth Abroad, or a Certificate of Citizenship are acceptable. U.S. citizens boarding flights to Mexico should be prepared to present one of these documents as proof of U.S. citizenship, along with photo identification. Driver's permits, voter registration cards, affidavits and similar documents are not sufficient to prove citizenship for readmission into the United States.
New Requirements for Travelers Between the United States and Mexico: Western Hemisphere Travel Initiative (WHTI) effective January 23, 2007, all U.S. citizens traveling by air to and from Mexico are required to have a valid passport to enter the United States. As early as January 1, 2008, U.S. citizens traveling between the United States and Mexico by land or sea (including ferries), may be required to present a valid U.S. passport or other documents as determined by the Department of Homeland Security. Ample advance notice will be provided to enable the public to obtain passports or passport cards for land/sea entries. American citizen travelers are encouraged to apply for a U.S. passport or the passport card when it becomes available, well in advance of anticipated travel. American citizens can visit travel.state.gov or call 1-877-4USA-PPT (1-877-487-2778) for information on applying for a passport."
http://travel.state.gov/travel/tips/regional/regional_1174.html
I don't have a passport, it's exactly how I got into Canada.