Just add it to the page you want the user to download, if you want a link in a page to download a copy of itself, you could create a link something like
<a href="myFileName.asp?dl=1">download this page</a>
and then at the top of the page (in asp), only write the header if the download parameter is set
If Request("dl") = "1" Then
Response.AddHeader "content-disposition", "attachment; filename=myFileName.asp"