Enter into find partners to battle.
Use the chat of the site.


Install the hamachi in HAMACHI folder
Open Hamachi and enter in the ID: "Pokemon Red Online Link"

Open TGB_Dual.exe
Click Options -> Folders  (Select the save folder correctly!)      (!)
Click File -> Netplay (select the player and opponent rom the same, Pokemon Red.gb)
If you are client, select client and in Server IP put the Hamachi IP of your opponent.


The save file is the same of the torrent: 
http://thepiratebay.ee/torrent/7011784/Pokemon_Red_Save_(All_151_Pokemon_Caught_lvl_100)
But this have all things needed for play online battles.