Why not just pick up a use set of OE 18" wheels, which are guaranteed to fit. Then pick your favorite winter tires?
There are a couple sets (M and non-M) in the "for sale" section right now for a very decent price:
http://www.zpost.com/forums/showthread.php?t=764925
http://www.zpost.com/forums/showthread.php?t=751194