ASP.NET Reponse.Content help with selecting and uploading file

Hi, I'm using asp.net and a gembox Excel DLL to read/write excel files. The writing aspect works well using the following code, which prompts the user where to save the file.

//ef is the ExcelFile object.

 Response.Clear();
 Response.ContentType = "application/vnd.ms-excel";
 Response.AddHeader("Content-Disposition", "attachment; filename=temp.xls");
 ef.SaveXls(Response.OutputStream);
 Response.End();

Now, I need to figure out how to read the file using the ef.LoadXls function. It works fine if I hardcode the file to the local machine, but how do I get it to prompt the user through the web interface and allow them to select/upload the file?

Thanks,

Terry