Front 18x9 +15
Rear 18x10 + 22
Tyres: No wider than 235 front, no wider than 255 rear (depends on height, camber etc but this is a rough guide)
Also, see this thread, heaps of info and pics:
http://www.skylinesaustralia.com/forums/topic/84208-wheel-sizes-offsets-for-skylines