Anon,
as far as I know you have to use the Office API to get this info. There is nothing, out of the BizTalk box, which retrieves this info – lots of file metadata – but not specific to Excel.
So, either you preprocess the file to extract the metadata and then pass that to BizTalk, or you write a custom adapter which does that. Writing an adapter is not something a beginner should consider doing lightly.
John D.