I'm running WinXP and the map editor loads about 8k RAM and gets stuck in permanent 99% cpu load without ever showing on screen. The only problem I have in the main game is not being able to use the Geoscape view with lights. I'm using 2.4 right now. The Radiant 1.6 works, except it gives the message that it can't load "ufos/entities.ufo".
Also, in the console:
ToolbarCreator: Failed to lookup command ToggleShowModelBoundingBox
ToolbarCreator: Failed to lookup command ToggleShowModelNormals