The full version you have to buy or download the student version. However the free version has just about everything you need for modeling. It's a pretty cool program and can be used for exporting models to Unreal SDK, CryEngine SDK and Valve's Source Engine (think Team Fortress 2, Left For Dead, Half-Life 2, etc).
Here is a link to Autodesk for the latest version (7.5 I think):
Softimage Mod Tools 7.5
or you can download the earlier version (6.0) which works better with Valve's SDK:
XSI Mod Tool 6.0
Not Uru specific, but it is a extra modeling tool at your disposal (can't ever have enough tools!!!
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