Reading an Excel file after upload

[Quan]

I am a beginner in ASP.Net and I need help.

I am trying create a page for user to upload an Excel
spreadsheet for me to read and do calculation on.

I used the <INPUT type=FILE...> for the user to choose the
file. After submitted, I can get
the .PostedFile.InputStream into a byte array, but how
would I convert that into a DataSet where I can loop
through and calculate my data.

Thanks.