Accessing BAPI structures in Excel

I am currently developing an Excel tool that calls BAPI_USER_GET_DETAIL to determine the user's firstname and lastname from the Export structure ADDRESS (BAPIADDR3). I am having trouble in how I should declare a variable to contain the contents of this structure and how to access the FIRSTNAME and LASTNAME fields of the structure. It seems that when I try to access ADDRESS as a string it returns a value of "Error 0". Any help here would help.

Thanks,

John