I installed UT2004 but I have to read how to make them again, I had to create the picts making screenshots in-game, now that I think about it, but that was for a water reflection, I remember now. The map I was doing, very small but OK, had a 40 foot-ish big puddle more than deep, got the reflection from my own cubemap, worked really good.
But there are other things I want or like to use from UT2004 in the editor, very useful .,,been a while so I have to read up on the cubemap thing again and working the editor again.
UT2004 is my poor mans Maya or 3DSmax,
But isn't there some stand alone program for making cubemaps, or just sides flat layout ? for skybox