Write excel file in C# 2.0 without using any third party dlls/interop/sdk

Write excel file in C# 2.0 without using any third party dlls/interop/sdk

I want to write a excel file (xls/xlsx) in C#.
Constraints:
I don't want to use following things while writing:
1. Third Party dll( My client is not allowing me to use third party dll )
2. SDK(Same as above reason as am not allowed to download)
3. Not allowed to use interop as in target server there is no office
installed.
4. OpenXml
Info:
1. Using VS 2005.
2. Using ASP.Net (C# 2.0)

Please suggest me how can I proceed.