ok here is the easiest way i can think of. take you workbook and open it up in Office X or better yet open it on a windows office. in office X just save as the files to CSV format for windows. just save as csv format in windows office.
ok after you got that. goto address book in windows and import then select import from other address books. select the csv (duh) and import you file. It will give the option of mapping each item which is a good thing. after that highlight and export your vcards. you maybe be able to do the same technique with mozilla on the mac, but i don't have mozilla installed. maybe someone has a better method?