When I try it, it always times out at 100 seconds. in that time it able to download between 29 and 31 megabytes
are you sure the time out is changing?
at line 1 add the following:
<%
response.write("Old timeout: " & Server.ScriptTimeout & "<br />")
Server.ScriptTimeout=500
response.write("New timeout: " & Server.ScriptTimeout & "<br />")
%>