Switching heads and head vs branch after CVS import

After having done a cvs import of Moodle using git-cvsimport-script all the cvs branches show up as heads. How do I switch heads within a checkout? cogito doesn't seem to be able to, and I'm unsure on how to do it with git.

And I am confused about the difference between heads and branches. Git and cogito seem prepared to merge across the heads (using cg-update for instance, when pointed to a different head merged it in, rather than switched to it), that would match a workflow where a group of people maintain very closely related heads and merge constantly across.

Branches don't seem to have the same expectation or support in the toolset. Why? What makes a branch different from a head, apart from the fact that they would be expected to drift further apart?

In any case, should the cvsimport turn cvs branches into git branches instead of heads? Is there are way to turn a head into a proper branch?

cheers,

martin