I just received a newsletter that announced a "Personal Learning Edition" of Vue 6 is availble for free. If you are not familiar with Vue it is software that is used to render beautiful 3D environments and landscapes.
The learning edition is free, but comes with a few limitations. However, it looks like a great way to introduce yourself to 3D. Some of the restrictions are:
For personal, non-commercial use only,You cannot exchange files with other users,Renders are watermarked and carry a logo, Render up to 800x600 without watermark for 30 daysYou have to register for an account, and then you can download the learning edition. It's available for both PC and Mac.