First of all - You need to download Office Primary Interop Assemblies
Office 2003 PIA can be found here
http://www.microsoft.com/downloads/details.aspx?familyid=3c9a983a-ac14-4125-8ba0-d36d67e0f4ad&displaylang=en[
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But before you start with interop you might want to know that due to security issues, you won't be able to access Office Interop when running on IIS server due to security issues with asp.net user (usually IIS_USER or something like that) Which runs using Network Permissions and doesn't have access to office interop.
You might search google for an alternative to create doc.
I think I saw an open-xml SDK from microsoft to generate docx files from code.