Hi Sgt Beaudry.
You move up in rank by scoring points. In Modern Weapons Custom Maps, where I see you've been playing, you move up in rank by getting kills. In a base assault game, you also score points by work that you and your team do on the bases. You also score a point in either game by healing a team mate.
You earn rank at 10, 20, 30, and 40 points. Each time you earn a rank, you get things added, such as more grenades, binoculars, etc. At the highest rank, you get artillery.
Not sure of your question about maps being corrupted, that should not occur. However, if you have custom maps in your /uo folder that are not currently being played on the server, you may get an error message when you try to join a server that you have bad pk3 files. If you move whatever file it tells you to outside of your /uo folder and restart your game, you should be fine.
You also might want to check out this post:
http://www.mobclan.com/forums/upload/index...mp;#entry154136Frag on!