When you get onto TribesNext.com go to the downloads page, and if you already have Tribes2 just click the multi-player patch title and that will open up the download file, save it (hopefully to someplace you can find) and then run it, it will ask you to accept terms of use and then you need to locate your Tribes2 folder, the default is C:\Dynamix\Gamedata, when you've located it you hit APPLY PATCH and it will patch your game, then you just run you game in online mod(properties, shortcut tab, Target: C:\Dynamix\Tribes2\GameData\tribes2.exe -online -mod Classic(or whatever mod you run) -nonpure)
If my explanation wasn't what you were looking for, you can look here
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http://www.tribesnext.com/forum/index.php?topic=37.0 <----