Id be interested to follow this too.
My Cobra alarm fitted to the Altezza is good but needs a few tweaks to get it back working 100%. In the instructions I have for it, it says that it can be used to do the central locking so at some point i need to tap into the electrics to sort that out too. Would be interested in other options too maybe but fitting a similar alarm system which has central locking function might be another option for you?
Have anyone fitted an alarm and hooked it into the central locking and can give advice please?