I'm looking for a Computer Aided Design tool that will let me plan out a floor of a house (looking down in a 2D way) plan out the walls, doors, add things like toilet objects, sink objects to bathroom, kitchen items into a kitchen etc.

Once the 2D plan is saved I will be able to look at the plan in a 3D environment, say a shot from one angle of the room.

A similar proprietory program exists, as my local DIY store used it to help us design our new kitchen. I want to be able to use a similar tool on a bigger scale.

Does anyone know if such a tool exists for Linux, or is there something siliar in develoment that I could contribute to? Failing that, am I going to have to write the d*mn thing myself?

You might want to check out Blender. It's not exactly CAD, but i think it's the best thing available for 3D at this time (except maybe for Maya, but that'll chew a few thousand dollars out of your pocket).