I've never done this, but I'm pretty sure that the server would need
to have the software  you require and that the admin would then have to
agree to you running  your own code, which I'd think is an unlikely
scenario.

I am not clear - there are many sites where you supply some data and
after they perform some calculation the result is returned in the
browser (for ex. on spot insurance premiums); So you think the xl
macro is the problem? in the sense that a hosting site would not allow
a protected xl macro  to run  on their server?

Check out these links

http://support.microsoft.com/kb/257757/en-us
www.sitepoint.com/.../php-apps-excel-worksheet-server
http://www.dbforums.com/showthread.php?t=1621729
gooled: running  excel macros on servers

I do not know of any website  that does this by means of an excel
spreadsheet. There are plenty of websites which use web apps to do this but
they are not spreadsheets.

Unless you own the web server (as distinct from using a hosting service) you
are not likely to have enough control of the server to do what you want with
excel.

If you do own the server you could set it up so that you could process any
spreadsheet uploaded  to a particular directory. You could then either
display information in the client's browser  or provide a link for them to
download the processed spreadsheet.

You would need a good knowledge of web server operation, the programming
language to be used on the server (e.g. php, ASP.Net, etc.) and VBA. If you
had this knowledge you might well decide that excel  was not the best way to
go for your project.

There are providers who enable you to use excel on a website. I do not know
if any of them allow you to use VBA.

thank you very much for clarifying this.