My apple script (applescript) just made a massive leap forward or at least my unerstanding of how people go about figuring it out. I never could work out how people new what all those scriptable properties where called until now.
Open Script Editor (/Applications/AppleScript/Script Editor.app) may be open a script you have been writting / downloaded.
The really clever bit:
from Script editor File-> Open Dictionary
Now choose the application you are scripting and you will get a browsable searchable list of properties that the script can get and set!