Yes, for applications other than 3DS Max and earlier versions of Blender, content is transferred using FBX. So, to make this work you'll need to first assess what you can make, which generally speaking means two things;
1) the ability to export FBX files.
2) the ability to use 'nodes' or 'null' entities.
If you have "1" but not "2" you should still be able to create simple accessory and furniture items as the meshes will still import using the FBX files internal skeletal hierarchy. If you have both it should be possible to make more complicated non-avatar based content; furniture and rooms with seating and possibly animation (to a degree).
To test, download the
the furniture example files and try importing the FBX files they contain, if all goes well you should see a simple mesh and a set of 'null' object representing the items overall skeleton - in Blender and 3DS Max these are 'nodes' and basically coordinate markers in the shape of wireframe cube primitives.
If you can import the FBX, and see the skeletons hieratical structure, try and export to FBX and see if that works. If it does you should then be able to import and assemble the result in IMVU.
Important note: the IMVU avatars are very large compared to the standard default scaling of both Max and Blender so when importing the FBX nothing may appear to have imported (clips out of the camera depth) and/or whatever is imported, DO NOT rescale or resize it, leave it as is to ensure its correctly scaled on import into IMVU.
