I created a file named x.csv with the following code.
<%
Response.AddHeader "Content-Disposition", "inline; filename=abc.csv"
Response.ContentType = "text/csv"
Response.Write "1,2,3"
%>

When I run this on a XP Pro web server, the filename in the Save As dialog box is correctly populated as abc.csv.

When i run on a Win Server 2003 web server, the filename in the Save As dialog box is incorrectly set to the ASP page name, x.csv in this instance.

Any ideas greatly appreciated.