If I remember correctly you can really only use an HiD conversion kit if you have headlamps with 'projector' type lamps, my Mk1 GS has them and I have converted to HiD, no problems at MOT time cos I have headlamp washer and manual levelling, both of which are pre-requisites for using HiD bulbs.
Most modern Audi's, BM's and Mercs have such kit normally with HiD's as standard.