First of all, lets just assume your name has anything to do with it
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If you want to start a single player map in Unreal, for example "Tashara1.unr", fire up unreal. While you see the flyby, press the tab-key. Type: 'open Tashara1.unr' [enter] and the map will load. Be sure you put all the files in the correct directories, the .umx files in the music directory, the .uax files in the sounds directory, the .unr files in the maps directory and the .u files in the system directory (of unreal of course). Incase there are more files, but them in the system directory as well (most of the times, that's were those files are supposed to be).
Another way to directly start a map is by double clicking on it. That's the easy way. As long as you put all the files in the correct directory, it should work.
One more thing, the map-pack Legacy wasn't made for Unreal, but UnrealTournament. Incase you didn't knew that. There are a few other UnrealTournament single player maps out there, be sure not to mix them up for regular Unreal maps.