What I have done is just copied my trinity folder to another folder... so on my hdd I have C:\Trinity and C:\Trinity2
To set you your second realm...
Open your database, go to auth/realmlist and add your second realm. You have to change your port number to something different than your first realm.
Now in your trinity2 worldserver.config file you have to change these settings....
RealmID = "the id of your second realm in the database"
DataDir = "the location of the maps, dbc and vmaps of your second realm"
WorldDataBaseInfo = "your ip;3306;your username;your password;world2"
CharacterDatabaseInfo = "your ip;3306;your username;your password;characters2"
WorldServerPort = "the port # you entered in the port column in the database"
Assuming I havent forgot anything restart your authserver, your worldserver and in your trinity2 folder you only have to run the worldserver.exe
Its been a while since I have done this so I hope I havent forgot anything.