Perhaps what you are trying to do is to take the original url ... which is dircted to an asp3 (.asp) page and rip out the querystring part of it and, from the original asp3 page redirect to an aspx page using that querystring.
So really, the code you need would be in asp3 VBScript and you merely append to a new url and redirect to the aspx page.
Well, just using querystring will grab the whole of the actual querystring, which you can then append to a new url.
In your example Request.ServerVariables("QUERY_STRING") should give you the string "PRODUCT=Product?Version=Version"
<%@ Language=VBScript %>
<%
response.expires = 0
Response.Redirect("http://yourdomain/testing.aspx?" & Request.ServerVariables("QUERY_STRING"))
%>
There are loads of things you can do to manipulate whats in the url address bar etc - see attatched file for some ideas.