Hi, I have the same problem on my VAUXHALL Cavalier 1.6i. I have to charge it up after about 2 days. I dont think its the alternator. It has a factory installed alarm - I have disconnected its horn, but the rest is still connected and the LED light flash. Sometimes I have noticed it is flashing as if the alarm has been triggered and so its relay is draining the battery.
Also, due to its age, possibly some of the components in the alarm are draining the battery- usually capacitor become leaky.
I dont know where to disable the power to the alarm, this would eliminate this possiblity.
CK, January 2008