I would recommend Bryce 5 as it can be found free and the version 5.5 which I use has some cool addons for it too. The basics are simple and it gives you an idea how to create and modify, which all 3d programs have the ability to do. Bryce is used all over and can be used in a wide array of designs and can beused in conjunction with other programs. Feel free to contact me here (eagle1original aka Anthony) or e-mail me
eagle1original@netzero.net. Best of luck, and remember "Genius is not how others see you its how you present yourself."