Ciao, ho proseguito ma mi sono imbattuto in un nuovo problema, una funzione con chiamata ad un typedef:
typedef struct
{
unsigned char TagType;
unsigned char AntNum;
unsigned char Ids[12];
}TagIds;
short __declspec(dllexport) __stdcall MultipleTagIdentify(HANDLE hCom, unsigned int TagType, unsigned char * Count,TagIds *value);

ho provato a tradurla così:
Type TagIds
TagType As Byte
AntNum As Byte
Ids(12) As Byte
End Type
Public Declare Function MultipleTagIdentify Lib "Reader.DLL" (ByVal hCom As Long, ByVal TagType As Long, ByRef Count As Byte, ByRef value As TagIds) As Integer

Che ne dici?