One must use more steps with the new Blender and IMVU software than before. Therefore, it's no long possible to create a short tutorial with just a few steps. The most basic beginners tutorial can be found here: DO THIS TUTORIAL AFTER DOWNLOADS
It is 4 pages. However, most of the space is taken up by detailed pics so it's not as bad as it may appear.
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Check to see if exporter imported by choosing "File" (top left corner). Then hover over "Export". Look for "IMVU Cal 3D export". If not there then do the following:
How to install exporter into Blender
After you have downloaded the zip file with this script start Blender.
Go to menu File (top left corner), User Preferences.
Choose "Add-ons" tab.
Click the "Install from File..." button located at the bottom.
Browse to the location of the zip file, choose file and click the "Install from File..." button.
Note: you don't have to unzip it first yourself.
Next click the checkbox for the "Import-Export: IMVU Cal3d export" addon to enable it. You will need to scroll down to find it.
Finally click "Save User Settings".