On Mon, Apr 28, 2008 at 04:50:20PM -0300, Victor Bogado da Silva Lins <victor@bogado.net> wrote:
> Is there any documentation about how those work?

Yes. There is a chapter in the user manual and there is the
git-submodule manpage.

> What I need is this, I have a already existing git repository, that have
> a subdir that could be seen as submodule (by this I mean that he is
> related, but could have a different commit tree). The git repository
> already exists and has many commits that apply to either the submodule
> or the main module (I would say that there is no commit that touch
> both). So is it possible to separate them easily?

Yes, see git-filter-branch.

> Would it keep my older commits? 

Not really, git-filter-branch will rewrite history, so the commit hashes
will change. Of course no code will be lost, but after such a migration,
people will not be able to easily just pull.