As has already been stated, AutoCAD _will_ do it, but it's far from ideal. I'd suggest looking into a "nurbs" modeller (like Rhino). Nurb surfaces are easier to get realistic complex curves (such as "cushioned" furniture). As far as rendering a lot of programs _will_ do it, but depending upon the quality you want from your renderings some are better than others. 3DViz (for instance) can do photo realistic rendering and is very, very nice. However, generally the better the required rendering the stepper the software learning curve. Although, once you get a high quality "scene/lighting" setup it's pretty easy to just switch out the furniture and/or change fabrics. If you're only looking for good rendering and don't require "photo-realistic" than most modelling packages will have it built in.
There's a ton of sites with downloadable furniture models (www.viz2000.com has a ton of good links to 3D sites). Maybe start off at www.e-interiors.net and download some of the cad files to play with if you want.