Just found this on the Steam forums:
This is an announcement to all America's Army 3 Players...
The Server Administrators for America's Army 3.x are looking to turn Punkbuster on for the servers to get the protection and control they need for the servers to keep the gameplay the way it is suppose to be.
For the Server Administrators to turn PB on, all players must manually update Punkbuster on their PC otherwise when you join the server you get stuck on the Team Selection and will not be able to play, then a little bit later you are kicked back to the browser.
Please follow the instructions below immediately to avoid having such issues when Punkbuster is finally enabled on the servers. Yes, you do need to do this as very soon most servers will have Punkbuster enabled and you will run out of places to play otherwise.
First download and install PBSetup from the following location: http://www.evenbalance.com/index.php?page=pbsetup.php
Once you have downloaded pbsetup just run it from any location and click "Add a Game".
Depending on delivery method and operating system it will be 1 of 4 paths. When you click "Add a Game" the path found is incorrect so you must browse to locate the "Binaries" folder, DO NOT SELECT "pb" folder as it is created or overwritten.
Paths are as follows
Deploy Client:
x86 (32bit) Windows
64bit Windows
Steam Download
x86 (32bit) Windows
64bit Windows
Again, make sure you have selected the Binaries folder and NOT the pb folder.
After adding the game, click on "Check for Updates".
When in-game, users will also need to click "Enable Punkbuster" on the MBS page America's Army 3.
Further support for admins and player can be found at www.airdaleops.com
