how can I determine if an excel file contains macros or not?

Goto:
Microsoft's product support page:
http://search.support.microsoft.com/kb/c.asp?ln=en-us&sd=gn

In the first box choose Excel97

In the second box type:
list all macros in all files

To answer your question, yes, it seems feasible that you could write a macro to open all files separately and then see if there is a macro attached.

Here are some other helpful links I've accumulated in the past few weeks:

http://officeupdate.microsoft.com/2000/articlelist/ExcelTips.asp
http://officeupdate.microsoft.com/articlelist/o2kExcelarticles.htm
http://officeupdate.microsoft.com/templategallery/default.asp
http://officeupdate.microsoft.com/welcome/excel.asp
http://support.microsoft.com/support/excel/content/vba101/default.asp
http://support.microsoft.com/support/kb/articles/Q254/3/65.ASP Advanced
http://www.cctglobal.com/outamioi.html
http://www.cof.orst.edu/net/software/excel/tips/dataentr.php
http://www.cpearson.com/excel
http://www.fontana.k12.ca.us/district/supt/technology/training/excelword.html
http://www.geocities.com/davemcritchie/excel/excel.htm#faq
http://www.geocities.com/geo_marksway/excel_solutions/excel.htm
http://www.indiatimes.com/infotech/help/tips/office/excel/
http://www.microsoft.com/office/excel/default.htm
http://www.microsoft.com/office/excel/support.htm
http://www.mrexcel.com
http://www1.fatbrain.com/partners/msoffice/excel.asp

I got it :) thanks!!

http://www.j-walk.com/ss/excel/tips/tip70.htm