Navigate to /etc and open the netbeans.conf file.
Add -J-Dfile.encoding=UTF-8 at the end of the line that starts with netbeans_default_options (make sure to include the leading space).
Restart Netbeans and it should be in UTF-8
To verify go to help -> about and check System: Windows Vista version 6.0 running on x86; UTF-8; nl_NL (nb)