you can open a document and save as html but as far i know office the html looks not very pretty.
see:
http://stackoverflow.com/questions/4923970/net-interop-excel-to-html
http://bytes.com/topic/c-sharp/answers/477965-excel-files-html-using-c
see:
http://stackoverflow.com/questions/4923970/net-interop-excel-to-html
http://bytes.com/topic/c-sharp/answers/477965-excel-files-html-using-c