They look a lot like the Warwic Premium Mesh.
http://www.tempetyres.com.au/content/products/bg_warwicpremiummesh.jpg
http://www.tempetyres.com.au/products_closeup.asp?part=&part_no=415
They come in 18x7.5, 18x8 and 18x9. Not sure of which offsets they come in or whether they are available in 4-stud, but a quick call to Tempe or one of the many other resellers would answer that.
In terms of 5-stud onto a 4-stud wheel, thats a case of square-peg-in-round-hole. You can re-drill wheels, but you wouldn't. Just buy a 4-stud wheel (specifically you want a 4x100) in the first place. The offsets available are most likely +45 or +40 in these wheels, or thereabouts. The standard offset on the Sportivo is +45. Very basically, the lower the offset, the further out the wheel will sit. ie slightly lower than standard = looks tougher than standard. Massively lower than standard = stupid looking and generally quite illegal.
If you ran an 18x7.5" +45 wheel for example, (bearing in mind that standard is 16x6" +45), you stick the outside of the wheel 19mm further out, and you get 19mm LESS clearance on the inside, ie closer to the strut. If you chose an 18x7.5 +40 wheel, they would be 24mm further out, and 14mm less clearance on the inside. Hope that helps a bit.
Then you have to choose a tyre, ie 215/35 R18, 215/40 R18 or 225/35 R18. So many choices...! As I understand it, larger wheels and tyres = slightly heavier steering, potentially slightly larger turning circle. Having your speedo accuracy change comes down to tyre choice, and getting your rolling circumference as close to standard as possible (standard is 620mm).
Shoot me a PM if you want some more help with this, as I did this kind of research before buying my 17s. Be mindful of the legalities of various aspects of changing wheels, like offset (which affects track), rim diameter and width etc. You will also need to consider whether your car is lowered, and any guard-rolling that may be required etc...
So much to think about...
Adrian