SL is effectively parameterized surfaces. Each parameterized object is a "primitive".
Both the planks and the windows I would build with a similar process. I would start either with the pre-mapped cube or with a gridded plane. The plane is easier, but doesn't have backfaces, which is okay for the planks but may-or-may-not be okay for the windows.
It's probably easier to show than to describe, so here's a video of a quick-and-dirty knock off to teach you how.
Model and Textures:
http://www.independentdeveloper.com/files/planks.zip
Video:
http://www.independentdeveloper.com/files/planks.wmv
If you start with the plane, give it four times as many grid sections as planks. (--Actually, four plus one, heh heh, I messed that up in the video, which is okay because it gave me a good chance to show you how to fix up the uv map which is something alot of people have trouble with.) If you need more edges or if you start with the cube, use divide loop to create more geometry. Scoot the vertices in to make the divisions.