The booleans in Bryce do not act the same way as they do in most modelers. Bryce Booleans only act upon how the light & material react to the shapes, they don't really change the shape but only "hide or reveal" the intersected space. Carrara actually tries to guess the intersected area and omit unrelated vertices and faces. Yes, if you manually remove vertices beforehand and then add more subdivisions in the area to be acted upon then your boolean will be more true. And, it will take you much longer to accomplish the goal (especially if you have to redo a couple of times. Frankly, for the extra time you will spend in fighting with booleans you could learn to use the Spline modeler to create that wall with a compound shape to make the window. I once did a boolean that took the machine about 1 1/2 hours to do. If I knew then what I do now about the Spline modeler it would only take about 15 minutes to create the object I needed from scratch. You are "stuck" with objects that you bring into Carrara though (like the Poser parts).