Editing for Unreal Tournament was great, because I could simply import my levels from Unreal 1 and modify them for Unreal Tournament. Not to mention I didn't need to learn a new editor. After most of my Unreal 1 levels made their way into UT, I started working on some new work, such as the Security Level from System Shock, the Aquilus Residence, and my MASSIVE Underworld conversion project.
To install a UT level, simply unzip it into the unrealtournament directory and the files should go in the right spaces. The maps should appear in the list when you go to start a multiplayer game/practice session.
If you are interested in making your own UT levels, I would suggest getting the latest patch for UT, which comes with UnrealED2, an improved version of the classic editor.