i remember when i put my central locking in. I had to do a lot of fiddling around to get it running perfect without any probs.. adjusting where it grips, where the actuators' mounted etc etc.. but it works out in the end.
With the security system: -it shouldnt be too hard. Just be careful when installing the bonnet pin and when hooking up the immobiliser to the ignition wire, dont wanna screw that one up! But apart from that, the other connections are to the central locking box, boot pin switch, door pin switch, shock sensor and of course the siren itself..
I find the best place to put a shock sensor is on the steering column. Thats connected to the wheels and thus has the best sensitivity !