I need to use excel as engine to compiute calculation.

The scenario is this:
1)A user click a link on the Browser.
2)IIS intercept the request and call the code that process
the request.
3)The code must create an instance of Excel, load a *.xls
modify some cell's value, force e recalculation and save
the *.xls.
4) Delete instance.
5)In the response send the *.xls to the browser.

This way to operate has same problems such as:
- Slow (because create delete instance)
- Sometime some instance remain active due to various
cause
...

I think that use directly Excel using Automation isn't a
good idea.

Someone have a good idea ?

Thanks All

PS: I use VisualStudio2003 and Office 2003