I am developing an ASP.NET web application. 

When the user clicks a link button in this application, the
application accesses an excel file and puts it in the http response.
Note that this file is not in the same folder as the application -
that is it is not directly accessible using a URL - you need to click
on the button to access the file. This is by design.

The question is this: when the user clicks the link he must click Open
on two download dialog boxes before the spreadsheet opens. How can I
setup the HttpResponse so that the user has to click once to open the
file? The file must not open in the browser window - but in an excel
window. I know how to do this on my local machine. What I need is a
way to avoid having to do this on all the user's machines locally.

Thanks

Here's the code anyways - I'll leave it up to you if you want to pay or not:

<%
Response.buffer = TRUE
Response.ContentType = "application/x-msexcel"
Response.AddHeader = 'Content-Disposition: attachment; filename="excel_file.xls"')

Dim vntStream

Set oMyObject = Server.CreateObject("MyObject.BinRead")
vntStream = oMyObject.readBinFile("c:\temp\tempxls.xls")

Response.BinaryWrite(vntStream)

Set oMyObject = Nothing

Response.End
%>

Opps, take out that ")" on this line:

Response.AddHeader = 'Content-Disposition: attachment; filename="excel_file.xls"')

Tried that already. Currently my code looks like 

Response.Clear();
Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("content-disposition", "attachment;filename=\"" +
filename + "\"");
Response.AppendHeader("Content-Length", fi.Length.ToString());
Response.WriteFile(fullpath);
Response.Flush();
Response.Close();

I have also tried 
Response.ContentType = "application/xls";
Response.ContentType = "application/x-msexcel";

all to no avail. the user is still prompted twice.

Make sure you're doing all of the following:
- use a GET request
- make sure the GET request ends with .xls
- use the "Content-Disposition" header in the response

I ran into this problem, myself.  When I changed the form's method
from a POST into a GET, the double dialog boxes disappeared.  See the
following Microsoft KB article for more information on this:

http://support.microsoft.com/default.aspx?scid=kb;en-us;238588