DevaintPC has made a little guide on UT2003 map creating :
If your one desire is to get a job in the games industry as a level designer, your one goal in life to achieve gaming nirvana with the perfectly designed UT2003 level, or you'd just like to get an understanding of what goes into designing a level then welcome to DeviantPC's first article that deals with the creative side of computing. If you've followed Alans articles (you have haven't you?) your PC should be running faster and smoother than ever, but what now? How about getting creative and exploring the possibilities offered by Unreal Tournament 2003's level editor, UED?