http://www.gumtree.com/p/cars-vans-motorbikes/4-custom-alloys-polo-saxo-corsa/1062327078 he says the holes are 100mm apartWhat are they from? See if they would fit by comparison of the numbers on this site: http://www.wheelfitment.eu/ . That should help.
There 185/55r14For the centre bore you'll either need spigot rings (if the hole is too big), or the flapwheel treatment (if the hole is too small). Micras have a 59.1mm bore IIRC.
What size rims are they? Will look good on the Micra, as long as they're not too big (13/14" suits these best).