That's a compile time option that compiles an XP specific version (which changes the BCrypt DLL uses) which isn't suitable as many customers have mixed tills (whilst they upgrade from XP to WIndows 7 tills). A given venue has to operate of a single EXE.
The functions used to replace the BCrypt ones works on Windows 7. However these functions are deprecated, that's why we prefer to use BCrypt instead.
Also - are they 64 bit compatible ?