If your unsure if you have an ipv6 assigned you can see it either in your welcome email or in Client area under vps in control panel area. If you do not have any ipv6 assigned submit a support ticket to the vpssupport department and well get one or more assigned for you.
example ipv6 is 2a00:1ca8:91::26c3:c24e replace this in the examples for each IPv6 your adding the gateway in examples is also what you should be using for the gateway.
 Centos 6 / Fedora 15:
   Edit /etc/sysconfig/network and Enable IPv6 support nano /etc/sysconfig/network then add the below    NETWORKING_IPV6=yes        Edit /etc/sysconfig/network-scripts/ifcfg-eth0: nano /etc/sysconfig/network-scripts/ifcfg-eth0
   IPV6INIT=yes    IPV6_DEFAULTGW=2a00:1ca8:0091:0000:0000:0000:0000:0001    IPV6ADDR=2a00:1ca8:91::26c3:c24e/128
   Edit /etc/sysctl.conf:
   net.ipv6.conf.all.accept_ra = 0    net.ipv6.conf.all.autoconf = 0    make the changes active sysctl -p
   Restart networking, and you're done!
   service network restart
====================================    Debian / Ubuntu add ipv6 addy       ip -6 addr add 2a00:1ca8:91::26c3:c24e/128 dev eth0       or     Use this command to append your IPv6 information to your network configuration file:
   cat >> /etc/network/interfaces <<EOF
   iface eth0 inet6 static
       address 2a00:1ca8:91::26c3:c24e
       netmask 128
       up ip -6 route add 2a00:1ca8:0091:0000:0000:0000:0000:0001 dev eth0
       down ip -6 route del 2a00:1ca8:0091:0000:0000:0000:0000:0001 dev eth0
   EOF
   Run the following command:
   cat >> /etc/sysctl.conf <<EOF
   net.ipv6.conf.all.accept_ra = 0
   net.ipv6.conf.all.autoconf = 0
   EOF    sysctl -p
   Restart networking and you're done!
   /etc/init.d/networking restart
============================= To test if its working you can use the below command ping6 ipv6.google.com
If you have any issues also ensure you have the ipv6 dns servers added nano /etc/resolve.conf
then add the below to bottom nameserver 2001:4860:4860::8888 nameserver 2001:4860:4860::8844
