The AC is located on the second floor (IIRC). It is very nice--good view of the tarmac, very spacious with a separate smoking area if you are so inclined, lots of seating, free high-speed internet computers, photocopier, printer, free open bar (tips not included), etc. If your laptop has a wireless card, you should be able to pick up a signal from the "Salón Internacional" on the next floor up (which offers completely free WiFi access).

In addition to the AC, I also have had luck getting into the Mexicana Business Class lounge on the 3rd floor by showing my PLT card. It's worth checking out--it has showers and an exercise room (IIRC), plus computers, drinks, snacks, etc. It is quite a bit smaller than the AC, however.