To play on the official servers with all features enabled, you must do the following.
Create a Strike Team account at www.strike-team.net.
Log into XWIS Control Panel, using your Strike-Team details. http://xwis.net/control_panel/
Add your serials.
Start the game as administrator.
Click Internet.
Click Custom Match.
Enter XWIS nick and password.
You should be able to play now.