Don't want to shoot your dreams down or anything but...knowing level design for UrT ain't gonna get you a job.
You wanna do level design professionally, you'll have to know either cryengine 3, or unreal engine 3, or source engine, or unity engine.
Those 4 aren't easy, scripting for unreal is difficult, but it's a must know.
Cryengine's SDK looks pretty damn scary when you first fire it up. A lot of possibilities.
Source engine and hammer can be very frustrating.
I haven't tried unity yet but i know uses some really great ways of making materials.
Out of those 4 i suggest you start with source engine.
Hammer resembles radiant. Some commands and entities will look familiar so it's not hard getting used to the world builder.
And there's a lot of games based on source engine that are really popular, some even free (Team Fortress 2).
Either way, you have a long road ahead of you, it ain't straight, it ain't easy, but with a lot of will and even more hard work it's doable.