Actually, programming manuals are available for most of the major alarm panels. However, companies like Brinks and ADT have their equipment locked up tight so you can't change anything. You should check out the Home Security Store
. They sell just about everything you need to setup an alarm system.
They will provide the manuals and even basic tech support for the system and/or sensors you buy from them. If you're not interested in buying anything, at least check out their forums. Lots of good information can be found there. Quite a few alarm installers frequent the thread to answer questions.
On another note, a monitored alarm does other things besides call the police department when someone breaks in. Most panels have a feature that will alert the monitoring company if you're having a medical emergency. Usually a button is pressed on the panel or on a remote to activate this feature. Also, do you have any smoke or heat sensors attached to the alarm? A monitored system will alert the fire department if one of those sensors is triggered.
NextAlarm and Alarm Relay are two of the larger internet based monitoring companies. Both have very competitive rates. I suggest reading this thread
to get a better feel for each of them as both have their pros and cons.