my xantia immobiliser can i bypass it?

hi i just bought this 1997 citreon xantia drove it home and noticed the 4 digit code in the book for the keypad immobiliser which was unplugged,,so it was plugged in and i tried it and it is the wrong code ,,,i cannot start the car atall ,,,is there a way to disable this,,im so pised about this i have a car that is perfect for what i need but now no dosh to fix it can anyone help atall with this ,,,i know it can be bypassed but i dont know how heeeeeeelp please
car is a citreon xantia 1.9td sx 1997
any help appreciated
thanks anyone
sean