Where offered W class is premium economy. So if you're flying British Airways, Virgin or British Midland for example you'll be seated in a separate Premium Economy/World Traveller Plue/New Economy cabin.
With most other carriers over the Atlantic W class passengers get no special treatment.
What airline have you booked to fly with?
Are you sure it's W and not V class, because as I indicated above W class is full-fare, whereas V class is a much lower-priced fare basis.