IMO, you say you aren't looking for a 3D program...but what you are really saying is you don't want something that's complex or hard to use.
Try sketchup and start small: make a 2x2 square, then "push" the face and turn it into a tube, now select everything and make it a component. Hey look, you just make a piece of metal tubing! Now make a copy of it (and make it "unique" to make it a "different" copy). Rotate it. Do that a few more times and wam bam you have a frame.
Its about breaking a problem down into small chunks. Take baby steps and incrementally add to your model. Don't know how to do something? Google it and I almost guarantee you the answer is there for you.
Take advantage of layers and hide/show to reduce the visual complexity and allow you to concentrate on "the next thing".
Have fun!