Here are the programming instructions for model year '97 - '99, which this remote should fit.
Pull the headlight flasher switch on to light the headlights, whilst on, turn the ignition switch to position one, let go of the flasher.
Flash the head lights four times and you will hear a beep. The system is now in learning mode.
Push the lock or unlock button on the first remote you will hear another beep.
This indicates that the fist remote is now programmed.
If you have only one remote you can stop hear and turn the ignition off.
If you have a second remote, press the lock or unlock button on that remote FOUR MORE times.
If you have a third remote press a button on the second remote only once and then the buttons of the third remote three times.
In this way you can program up to five remotes. After the first remote, you must press remote buttons such that the total number of presses equals five.
I?ve used this method a number of times without fail it works on X308 (XJ8) cars
There are other methods for different models of Jaguar (X300, XJS etc), which revolve around using the Valet parking switch instead of the headlight flasher.
www.jag-lovers.org has them all listed in the X300 forum. I can also recommend this site as a veritable wealth of information.
Good luck
Lenny
my car is a 2001 xj8,i know this works,causr i have just done mine