if you look on the
multiecuscan site it tells you exactly what cables you need, I kinda disagree with g8rpi on what you need, pretty sure I am right but wage in g8rpi is i am wrong somehow.
this page shows all the cars it can connect to.
http://www.multiecuscan.net/SupportedVehiclesList.aspx
scroll down it and it has a load of codes in coloured boxes showing what you need to connect to different parts of the car.
I have zero experience with actual cabrios and they are not seperately listed but they are basically just a P85 16v as far as the ecu is concerned (assuming its not a 1.6 90, pretty sure you have 1.2 16v one). That means it has a 18FD ecu and all you need the KLL/Vagcom lead and a 3 pin adaptor.
The 3-pin to OBD adaptor is not in either of them kits posted already - what i used on my old 85 ecu was this
http://www.ebay.co.uk/itm/291215844541
So the 3-pin adaptor connects to the diagnostics port on the engine loom (right near the ecu, usually has a little cap on it to stop crud getting in the contacts), and the little red and black crocodile clips connect to the battery, the the big plug to the KL cable and the USB on the other end in the laptop.
Connect all the wires, turn the ignition on (car doesn't have to be actually running but you can do it that way too and monitor all the ecu inputs), open
MES and top left select fiat, then on the right scroll down to Punto 85 16v, bottom left box make sure its on engine and then the bottom right should have 'Magnetti Marelli IAW 18FD Injection'
like this:
View attachment 172430
Then press connect, it pops up some boxes about keys, just press yes. I have noticed over the years that sometimes it says make sure the key is off rather than ignition on position which is wrong, you have to have the ignition on always so the ecu actually is powered up or it can't connect.
Also, depending on what you want to do you will prob be ok to just have the free version, it can read and clear codes, it can even datalog albeit with limited channels. I only ever had to buy a licence when i started trying ot use it on newer cars like my 500 and my old alfa 159, you will prob be totally fine with the free version.