im back

from my experience i recommend When modelling your model you should have the separate parts grouped together. otherwise you will probably have texture problems. this is also the case with entities.
according to this .fps file you have three meshes. 2 Wall.x meshes and a floor.x mesh.
they are textured with wall2_D2.dds and floor2_D2.dds they are all rotated some way and are csg immune.
(doors cant be cut into them.
If the above information seems correct and those are the names of your meshes and textures then i don't see a problem. if not can you provide the paths, names and file types of all the parts.
If you wan't i can put it all together for you. i'm feeling nice today.
as for my stairs i have it figured out. thanks for asking though.
EDIT
oops. ive just noticed that the problem is solved. NVM
http://sites.google.com/site/jordanz2010/