Texture Offset on floor and ceilings

I'm working on making a capture the flag map, and in one part of it I have big trees as the bases. The problem is, the texture for the trees, JNGWDF2B, isn't lined up correctly at all. I can't figure out how to offset the texture so it is the correct size and in the right place. Please tell me there's a way to do this?

http://wiki.srb2.org/wiki/Flat_Alignment should be what you're looking for.