Here you have a little tutorial about the right steps to install Blender. For Blender to work, and most important thing, to export i3d files, you need the right version of Python compatible with the right version of Blender and, of course the export plugin.

After you download the archive, proceed to install following this steps:

1. Install python-2.5.2.msi
2. Extract the Blender 2.4.9 from the zip file into a folder. Its enough to extract it, there no install needed.
3. Extract and copy blenderI3DExport.py into /your folder where you placed the Blender/.blender/scripts

Now start the Blender (double click on Blender.exe in the folder where is placed) If everything worked fine, now you should be able to see in File / Export the i3d file type.

Happy modeling !

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