Adding a Save As pop-up to an ASP.NET web application that generates html documents..

I have an asp.net application that generates html documents based on a user's information they have entered into textboxes.  The .html file is automatically downloaded to the user's LOCAL computer using the following:
Response.AppendHeader("content-disposition", "attachment; filename=MyNewFile.html");
Response.ContentType = "text/plain";
Response.Write(DocumentMadeByApp.ToString());
Response.Flush();
Response.End();
This works great.  BUT.....what would be better is if a SAVE AS window popped up prompting the user to save the DocumentMadeByApp (see above code) to a folder OF THEIR CHOICE.  
Even better would be if there is a way for an ASP.NET application to AUTOMATICALLY save a file to a particular directory assuming read/write security measures could be implemented to allow for the writing. 
But I would settle with the SAVE AS pop-up if anyone knows how/if this is possible?
Thank you for your ...