Here is the way to simply install JNC (Juniper Network Connect which is the Juniper VPN client) under ElementaryOs or Ubuntu
1/ Installing Oracle Java and download the Juniper software
If you're under a 32 bits version (uname -a => i386)
natjohan:~$ sudo add-apt-repository ppa:webupd8team/java
natjohan:~$ sudo apt-get ...