Boy I had problems with getting this to work earlier. But the solution was simple when I got to know it.
It's just as simple as you need to set the tomcat service to run with a account name and password that have access to the folders in question.
Use the "Settings->Control Panel->Administrative Tools->Services" tool and change "Apache Tomcat" properties and go to the login tab and set a username / password that you want all tomcat applications to use.
Stop the tomcat process.
Set username / pw
Start the comcat process.
WARNING. Do not use the Configuration menu from the tomcat tray icon to set the username / password. I tried to set it there several times without any success. Looks like you can read out the current settings there, but you cannot change or set it.