Switching branches without committing changes

He all,

I'm still a newbie to Git (and this list), so if I don't provide enough details please let me know what you need and I will provide :).

I'm trying to switch branches without committing my changes. Is this possible? For example, I'm working on a site, I'm testing the implementation of a new technology (branch B), I'm not quite done there (or I forget to commit everything) and I want to implement something else new. I create a new branch off of B, called B.1, and then make some changes. I commit only the changes that apply to B.1 and then try to go back to B. However, I get an error saying a file I changed in B is not uptodate and it cannot merge. What am I doing wrong and how can I get back to B?

Thanks all! Joe