Using the excel.application worksheet.saveas method you need to know the constants
Ron mapped file extensions to FileFormat constant his site:
File Extension ".xlsb" --> XlFileFormat= 50 File Extension".xlsx" --> XlFileFormat= 51 File Extension".xlsm" --> XlFileFormat= 52 File Extension".xls" --> XlFileFormat= 56 File Extension".csv" --> XlFileFormat= 6 File Extension".txt" --> XlFileFormat= -4158 File Extension ".prn" --> XlFileFormat= 36
full list of XlFileFormat Enumeration
