As in the title:

Is it possible in "The Sims 1" to create custom 3D meshes and animation data somehow?

I know that it's quite easy to change texture images for existing objects (once I've done it the hard way, by hex-editting the data files; now I know there's Transmogrifier for that). But what I need is to create custom characters (non-human; that's why I need to mod the entire 3D meshes and animations too). Is such thing possible?

If there's such possibility, please direct me to some places where I can read about it or software I can use to achieve it. Maybe some documentation for the file formats and data structures involved?

I'm a nerdy programmer, so don't be shy to post technical information.

Simblesse Oblige has a lot of useful stuff.

http://simblesseoblige.com/viewtopic.php?t=514

And SSoW have tutorials too.

http://www.woobsha.com/diyworkshop.html

You'll probably tear your hair out trying to find a copy of IFF Pencil so here's a link to where I've uploaded it.

https://www.box.com/s/oathjcz7vt9lcymyx54y