It's not something I would ever suggest someone really relied upon - but in a scenario, SQL will always go through the select clause one by one.
Of course, the way that it prepares the data it needs to do those calculations (ie, ordering of joins, that type of thing) may change according to the statistics. But you can generally rely upon the select clause.
Hope this helps,
Rob
Rob Farley
LobsterPot Solutions & Adelaide SQL Server User Group
Company: http://www.lobsterpot.com.au
Blog: http://blogs.lobsterpot.com.au