It differs from Punto to Punto.
Working on the assumption you are getting the correct offset and low profile tyres you maybe able to 17" with no rubbing, 16"s are your best bet but even if the 17"s rub you won't need to do anything to the arch, its a case of trimming a bit of plastic from the rear bumper and maybe removing a screw.
It is pointless going for 16's as they are only slighty smaller than 17's because the tyres are bigger. The ony bit of work i had to do when fitting my 17's was to trim the inside of the bumper slightly. It was no trouble and took me about 10 mins.
