To do this double click the vl2 file and then find Winzip in the list of programs. Feel free to look at the code for my scripts, its a great way to learn about scripting or for making private modifications. If you wish to release a modified version of one of my scripts or your script contains a large part of one of my scripts please ask for my permission first. The best way to learn is to look at other players scripts to see what they did. Of course don't just rip the code, learn from it and write your own.
Scripts are just text files but with a .cs extention.
You can also put the script in a vl2 file, you need these same directories but inside the zip. What I do is make the directories in a temp folder and then put the script inside. Next rename the zip a vl2 and slap it in the base dir. GUI stands for Graphical User Interface, its what you use to play the game. In Tribes 1 doing a gui was difficult as you had to create, save and then load them using the in game editor.