How get to code behind a custom button?

I have a machine running Excel 2000 on WinXP. Every time I open any workbook in Excel there is a customized button that has been added to the Standard toolbar. I need to re-create what this button does in Excel on another machine. I know the button causes the execution of some macros located in various files.

At first I tried finding a file that tells Excel about the customized button and supplies the code behind the button. I searched Excel.xlb and Personal.xls and I can find no macros for the buttons. There is nothing else in the XLSTART folder. I searched the c: drive for .xlt, .xltm, .xltx files and found none.

When I look at the macros in a fresh workbook that has this button there are no macros and no VB code. How can I get to the code that executes when the button is clicked?

Thanks.