Fit the entire lupo dash It would take great skill to make it look anywhere near decent on a mk 1 Arosa, given the hacksawing you'd have to do.
stator's post in lupo key was marked as the answer
They all have transponders in the key. You can remove the transponder from the old key and put it in the new key if the new key has the space for it. To take the old key apart you stick a small flat screw driver in the hole around the edge. The key with a small light is easier to take apart. If you get new keys with transponders you can also have them programmed to the car, but you will probably have to pay a locksmith to do this using a computer. You would also want to make sure you get the same physical cut for the key so it works your doors and ignition. You would probably have to declare after market central locking to your insurance.
stator's post in Double DIN in a Mk1 Arosa was marked as the answer