i have some panasonic cameras too (thanks, martin), and it's not terribly easy to do what you are asking. obviously, the cameras don't know anything about the alarm. taking periodic pictures on the cameras means accessing a dynamic (in the sense that it changes) url because the picture index is incremented on each rule when it is taken (i.e., you don't know the index of the latest picture).
the way i implement this (and just recently) is through homeseer. it knows the status of the elk because of the elkm1 plugin, and the recently implemented netcam plugin which can take pictures as an event action. note, you have to take two pictures with a camera to get one of them cached (it doesn't cache a picture until there is one to replace it). from there, it's a script to find the newest picture in the directory from the right camera and email it. but i think that functionality is being built into the next version of the netcam plugin.
of course, i don't know if powerhome has the same type of capabilities.