More details would help, but look at-
http://www.automotiveelectronic.co.uk/cars/renaultimmobiliser.htm#renaultimmobiliser
http://www.remotekey.co.uk/cars/renault/
http://www.immobiliser-unlock.co.uk/id1.html
Never used any of them, dont know if they're any good, plenty others available.
bill
June 2011