Do you want the data in an actual Excel spreadsheet (which would require ActiveX calls to Excel) or into a file such as .csv which can be opened by Excel?
Both parts of your question, (RS-232 data read and data to Excel) have been asked and answered countless times on these discussion forums. Please try to search the forums on these topics and you will find numerous examples. If you still have a problem, then post a specific question with the code that you have written that is causing you a problem.