No cheats interior half-walls
A no cheats method for creating interior desk-height half-walls. The limitations are the walls are not load bearing, however they can butt up against, bisect or be bisected by normal walls.
Interior half-walls completely without cheats
The only real restrictions are the half-walls must be interior walls and upper floors, and roofs cannot be placed till after the half-walls have been placed. Also, if you place the half-wall against an exterior wall part of the original texture will bleed through to the outside (you can hide it with shrubs or objects). Unlike other methods for building half walls these walls are at fixed heights and are not load bearing.
Lay out your foundation as normal.
Using "Roof Types" sellect "Shed Gabled Roof" and place a one-tile-wide roof with the high side at the location you want your half-wall to appear.
Completely enclose the area which will contain the half-wall. It will ONLY work in an area the Sims 2 sees as an interior space.
Place a roof above you almost complete half-wall.
Delete the slant walls that were once the sides of your roof...
...and you now have a fully functional desk/table height half-wall with no unusable areas around it.