2 questions with DirectX

[NecroDOME]

Im building a game in 3D ( UnDelphiX )....
Now im a little stuck building a 3D editor.... I can make rooms etc... My

My 1st question
If I make a room, and I create an other room next to it (2 room hit achtother), I need to cut some polygons, so you can see the other room....
Has anyone got a method for it
(ist something like the boolean-function in 3D max I mean)

my 2nd question : how to put decals onto walls ...

:?: :?: :?:

[Zanthos]

A decal is basically a textured quad that lies parallel to its parent wall. You should leave a small gap between the wall and the decal so that there isn't a power struggle with the depth buffer, or you'll get all sorts of choppy lines on the decal. I'm not sure on a value, you'll have to fiddle around