Well, I guess you could try
Zmodeler2 homepage. Check the Docs section. Here's a really small tutorial
http://www.etspe.ca/zmt/v1/. It's old but it's a nice start.
There are lots of nice tutorial in french if you speak french or if you don't mind Babelfish and friends.
Edit: oh, and if you're trying to make models for a particular game, you might wanna check those game fansites and modding communities. Sometimes they have nice specialised tutorials too.