This should give you an idea of what you need to do

http://support.microsoft.com/kb/302096
http://www.devx.com/dotnet/Article/42590

Basically, the .NET namespaces are wrappers around the COM calls.

>Hi,
>
>I need to analyze some data in an Excel worksheet and then modify some of the existing cells, and then also add new rows of data to the Excel worksheet.
>
>Historically, I've been using VFP and COM to do this task. But now I'm looking to upgrade my process to .NET. (Either C# or VB in VS2010).
>
>Is COM the recommended way to do this from .NET? Or does .NET have better ways to manipulate Excel?
>
>And... does anyone have links to any sample code that might get me going in the right direction?
>
>Thanks,
>Guy