A B737-500 flight crew experienced loss of cabin pressure; executed an emergency descent; and diverted to a nearby airport.

Narrative

Enroute at 36;000 FT our cabin altitude warning horn activated. We both looked up to find the cabin at 10;500 FT with the cabin climbing at 1000 FPM. We donned our O2 masks and established communication. The decision was made to start an emergency descent and divert. We had a jumpseater that was able to help with checklist items and getting our charts out. As we started down; the Captain switched the packs to high. Later in the descent the cabin stabilized at around 10;000 FT and indicated a 500 FPM descent. In the descent we had to deviate around a few rain showers and got struck by lightning. Captain was busy talking with the flight attendant's; Dispatch; ATC; and the passengers. We were very happy to have a jumpseater (Company First Officer) to help. Training really took over and we just handled the situation. Later we thought about the situation and decided that we had no time to troubleshoot and took the safest course of action. Aircraft had previous write-ups for pressurization problems.