run excel macro using vbscript

[redree]

I have an excel sheet "project.xl sm" with a macro "add" that update a cell value.
i want to run the macro using vbscript externally.
the important thing is i don't want to vbscript to open the workbook or close it as i will be openning and closing it manually, the vbscript should only run the macro.
any help please

[ghostatinstruct]

I have a very similar problem, I want a Visual Basic 2005 program to run a macro in Excel 2007. I have googeled for days, but all I found were Solutions, where the workbook was opened or a new workbook was added. The problem is, the workbook should already be open (manually opened) and the VB program should only trigger the macro, but not reopen the whole workbook!
I would be very happy for any kind of ideas!