Hi Kishore,
You need to append to your URL a field that exists in your list. In my below example City has to exist in my list and has to have a value.
http://google.com/maps?City=<%City%>
If your selected list item has the value of the column City equal to NY then the new URL would be
http://google.com/maps?City=NY
Our documentation explains this feature, please give it a try.
If you're on Quest Web Parts 5.7 for SharePoint 2010 then you have the option to open the new dialog in a new window, dialog or current window.