The 16" ones fit on 18" wheels, but the length between the indentations (where the lug nuts go) is larger (i.e., you won't be able to get a 22mm socket on the lug nut w/o rotating the center cap a little).
Yeah, the 8/02-current are 18's. 98-7/02 are 16's for the LX. I think the LC came w/ 17's w/ optional 18's, but I'm can't say I've even seen 03+ LC's in this country w/ 17's. They seem to all have 18's (maybe one of those nickel & dime mandatory dealer options that drive up the price of the LC to be about the same as the LX?).