I second the statement on getting a car and driver from the hotel. Also, keep the following in mind:

1. At Mexico City, if you are going to convert pesos at the airport, watch your valuables carefully. Many thefts can take place at the currency exchange windows. IME, the rates are better there than in the US.

2. Go to the registered airport taxi window, last I recall, it was to the far left of international arrivals and get a voucher for the cab to take you to your hotel. DO NOT take taxi rides from the many helpers who will try to offer you a ride.

3. Do not walk alone at night anywhere, even men should follow this rule.

4. At restaurants, if you do not have your car and driver, have the restaurant call a radio taxi for you. Don't go hail a taxi on your own.

Notwithstanding all of this, Mexico City is a great place to take a weekend trip. The museums, restaurants, pyramids, the zoo all make the time worthwhile. Great people watching is available on Sunday am in the Coyoacan area and the Frieda Kaklo house is walking distance in that neighborhood.