They will not fit on regular X5 as is. Rear wheel bore size is smaller on the wheels than regular X5 bore size. You will have to increase the hub/bore size on wheels for them to fit.
Canadian ebay listing
BMW X5 M,X6 M Models Winter Tire Package Style 298M on eBay.ca (item 170395000448 end time 10-Sep-10 13:45:35 EDT)