Softimage Mod Tool (previously known as XSI Mod Tool) is a free version of Softimage that can be used for Non-Commercial purposes. If you are looking to learn how Softimage works, Mod Tool is an excellent place to start... but it does have some important limitations.

-It is not intended, nor allowed to be used for Commercial purposes.***
-It does not allow normal Softimage scene file (.scn) saving.
-Instead it will save scene files as (.exp) which are not compatible with full versions of Softimage, by design.
-It is limited in it's rendering capabilities via resolution limits and watermarking, but Ultimapper rendering may work.
-There is no official support from Autodesk other than online documentation.
-(other features such as Syflex cloth and Hair may be limited as well)
***Mod Tool Pro can be used for commercial purposes if you are an XNA Creators Club Premium member.
***Further info on this can be found here.

Definitely read over the EULA through the above link if in any doubt about how Mod Tool should/can be used.

Other than that stuff, Mod Tool is a fully functional version of Softimage 7.5. Ready for learning/test driving or admiring at your leisure. A great place to get some great Softimage learning materials is here and its all free!

Mod Tool was designed primarily for aspiring game development artist's to use for content creation and "modding" content for existing video game engines. It comes ready to export FBX and Collada files, and can also support file exports for Crytek CryENGINE® 2, Valve® Source™ engine, and Epic Unreal Engine 3 using a variety of plugins.

If anyone has any additional useful info or resources regarding Softimage Mod Tool, please continue to post. If you have questions, it would probably be best to start a new thread.