I am more than sure that the UK clubsport is supplied with 18inch wheels. We don't have any brochures yet, but my local dealer had more details on his internal intranet. It showed a picture of the wheels and confirmed that they were 18inch.
Checkout the research section of icebergcars.com - the importers I am using to source the car from Germany - I make a 15% saving on the UK list.
I've got pictures of the style 71 wheels too, and they are available from circle BMW on: -
http://www.circlebmw.com/parts/wheels/dscw71.htm
As you can see the standard fitment is 18inch on the E46.
I think that the wheels will be slightly modified from the aftersale wheel. Almost definitely the wheel will have the 'M sport' badge. This would of course make then more exclusive - BMW UK have confirmed that they are only available for this model.
I must admit I am certain on the size of wheel - but less so on the design. If you get any more information I'd be grateful.
What worries me is that the car will be available with optional 19inch wheels like the M3 - and if so I'd rather get those.