Setup Self-Hosted VPN that allows 5 simultaneous users (iPhone/iPad + PCs)

We are looking to host a VPN solution that will allow up to 5 simultaneous user including iPhone or iPad users. We'd like to setup the VPN in two locations so we can do box-client and box-box VPN. Hamachi is not an acceptable solution. This must be done via freeware open source, we aren't looking to purchase a commerical product. There will be two dedicated boxes for this effort - I will build out the boxes and OS and will give you access to configure/test them. You get to choose the OS, VPN software, etc. When you make your bid, please let me know what your selection is so I can base my decision on your method. You do not need to give specifics, for example, you can say VPN on Linux or VPN on Windows, etc. If you have any questions, please let me know. We do not have static IP, but we do have a premium dyndns account.