The VPN Host / Joiner must be accessible from the Internet. If you don't have a static IP you either need to communicate your current IP at the time you want to join / someone wants to join the VPN (Difficult) or use a dynamic DNS service that allows you to associate a name with your computer.
the thing is that i have a static ip but it is not accessible from the net as it is the NAT ip given to me by my Broadband bervice provider and he is not giving me any kind of ip that can be accessible from the net. in this case if i want to use the VPN service is it possible
If you are joining, I think it should be okay (Although there 'might' be a problem with the tunnel setup). If you are hosting you'll need to get your broadband service provider to forward the connection to you.