Autodesk, auto CAD, and 3dsm are all for people who pretty much know what they are doing. If you don't already know how to use those programs like the back of your hand, i would not recommend trying to take up interior design through the use of them.
There was a program i had a LONG time ago that basically let you build a house from scratch and had preset models to use. It was an easy program to work with (it was about 6 years ago, i was 12, so when i say easy, i mean it). If i can find the name of it i'll get back to you. If not, then you at least know it's out there