Well, importing this or that COM type library, which is what importing dll is really about, has nothing to do with Windows version the compilation occurs in, as well as Platform SDK version.

These are interfaces that msxml3.dll has impelented compared to msxml6.dll:
Code:
struct __declspec(uuid("65725580-9b5d-11d0-9bfe-00c04fc99c8e"))
/* dual interface */ IXMLElementCollection;
struct __declspec(uuid("f52e2b61-18a1-11d1-b105-00805f49916b"))
/* dual interface */ IXMLDocument;
struct __declspec(uuid("3f7f31ac-e15f-11d0-9c25-00c04fc99c8e"))
/* dual interface */ IXMLElement;
struct __declspec(uuid("2b8de2fe-8d2d-11d1-b2fc-00c04fd915a9"))
/* interface */ IXMLDocument2;
struct __declspec(uuid("2b8de2ff-8d2d-11d1-b2fc-00c04fd915a9"))
/* dual interface */ IXMLElement2;
struct __declspec(uuid("d4d4a0fc-3b73-11d1-b2b4-00c04fb92596"))
/* dual interface */ IXMLAttribute;
struct __declspec(uuid("948c5ad3-c58d-11d0-9c0b-00c04fc99c8e"))
/* interface */ IXMLError;
struct _xml_error;
enum tagXMLEMEM_TYPE;
In case your code does mot make any use of these, it must be indifferent to what exact dll you import on compilation phase.