> Sign up for Logmein Hamachi.
> Create a network. (Network Name: (Any that you like), Network Type: Mesh, Click Next, Join Request: Automatic, Password: (If you keep one, you'll have to tell it to everyone)
> When you create the network, you will be given a network id. (write that down somewhere)
> Download and install Hamachi on all computers that want to play the game.
> Once installed, run it and click on Join Existing Network, Provide the network id and the password (if any)
> Once every one has successfully installed and joined the network, you'll be able to see them in the hamachi interface. (Ask everyone to disable the firewalls, to avoid issues.) You can right click on any Online PC and click on ping to check if the connection is Ok.
> Now to the Red Alert 3 Part. Go to Settings > Network > and set the adapter to the one which refers to Hamachi. (No need to change anything else.)
> Host a multi player game / server (the one with the best internet should host it to avoid lag.
> Other players will see the created server in the game list.
Note that in the steps above, any ONE person will create the Hamachi Network and EVERYONE (including the one who made it) will join the network.
ONE person will make the server and EVERYONE will join it.
EVERYONE to disable their firewalls.
EVERYONE to change their network adapter to Hamachi in RA3 settings.
Hope that helps.