You mean that adding a texture to a surface suddenly closes UEd? If so, that means you need to download UnrealEd Fix 4 or more preferably download the newest patch for UT (patch 521b). If you have problems importing textures, you must take consideration that the image must be in PCX format, 8-bit or 256-color, and must be in 256x256 pixels, 512x512, 128x256, 64x256 so on and so forth.