what key do i use to switch back and forth with languages???

I've never seen an easy keyboard shortcut for that, either, so I've resorted to displaying the language flag in the menu bar with four preset favorites available.

To change my input between Canadian and Canadian French, I use Shift+Command+Space. This can be configured in System Preferences> International>Input Menu, then Input Menu shortcuts. By default, in Tiger anyway, it's set to the same as the Spotlight shortcuts, which are used instead, so you do have to change them.
EDIT: Sorry, you can't CONFIGURE the shortcut there, it simply lists them. There should be a Keyboard shortcuts link. Clicking it should bring you to Keyboard shortcuts, where the Input Menu ones can be changed. 🙂