I am a dev for IMVU but as of yet I don't actualy mesh, I only retexture meshes that other people have alreay created. I have had a go trying to mesh for IMVU and I found it a bit complex trying to export it, this is mainly because it has to be exported into a file called Cal3D.

I know that the free software "google scetch-up" doe allow you to export to IMVU if you export it as somethingorother 4 (sorry if thats not very specific but all I can remember is that you can export it into 2 thing and the one that works has a 4 on the end lol). scetch up isnt actualy that good for meshing anyway as it is EXTEMLY basic. you may find this link usefull "http://www.imvu.com/catalog/modules.php?op=modload&name=phpbb2&file=viewtopic. php&t=38449&highlight=making+beat+boxes"

I have also heard that blender can export into Cal3D if you can get the script working for it, I have tryed and as yet I havn't managed it. (I am actualy not that fantastic with computers). you may find this link usefull "http://www.imvu.com/catalog/modules.php?op=modload&name=phpbb2&file=viewtopic. php&t=14052&postdays=0&postorder=asc&start=0"

I know for a fact that 3D studio max does export into Cal3D but if you google it and look up the price you will understand why that is not at the top of this list.