Driver goes in this folder, as you tried before...
jasperreports-server-cp-4.7.0/apache-tomcat/webapps/jasperserver/WEB-INF/lib
The one step you did not list above is an important one.., restart Tomcat after you place the driver into the folder.
I got it working just a bit ago. Also see this link...
http://www.rhyous.com/2009/10/27/adding-a-sql-2008-server-as-a-datasource-to-jasperserver/
I basically just followed steps 1-4 on that page, I did not figure out how to enable the admin user for Tomcat though (so I can access Tomcat's 'manager' and restart it easily, I'll fix that later).. so I just restarted the computer, which restarted Tomcat, so I could get back to work quickly.
