A database created with one of the new sort orders will not open in Access 2007 even with Service Pack 2 (SP2) installed.
There is a list of compatibility issues : http://msdn.microsoft.com/en-us/office/cc907897, which includes sort order, however the big gottcha is not stressed, and that is General sort order. This is not the same as General sort order in previous versions of Access, it is new. For compatibility, you must choose General Legacy sort order.