You can't actually do this. (Security issue.)
But you can create a link that performs a download. It is a bit complicated, because you cannot force a browser to obey you, and it might try to just display the file instead, depending on the settings of the user's machine.
6 and IIS, this is what I do in response to a link click
on <a href="http://MySvr/MyApp.asp?wci=Send_File>Download File</a>
Private Sub Send_File_Respond()
On Error GoTo Er
Dim pth As String
Dim strDoc As String
Dim CntTyp As String
Dim fSize As String
Dim oStrm As ADODB.Stream
strDoc = "StandardMaterials.txt"
CntTyp = "text/plain"
pth = " . . . " ' Whatever you need here
Set oStrm = New ADODB.Stream
fSize = GetFileSize(pth & strDoc)
Response.Buffer = True ' Turning on buffering & clearing ensures that
Response.Clear ' all of the header information will be at the
' top. Feature of IIS 4 and on.
oStrm.Type = adTypeBinary
oStrm.LoadFromFile pth & strDoc
Response.AddHeader "Content-Disposition", "attachment; filename=" & strDoc
Response.AddHeader "Content-Length", fSize
Response.ContentType = CntTyp
Response.Charset = "UTF-8"
Set oStrm = Nothing
Rs: Exit Sub
Er: ' Report or log the error here, if there is one...