As others have mentioned, list and related list support are coming out in the Orlando release, but I don't think that's what you're asking about. It sounds like you're asking if you can click on a form tab through an ATF test. The short answer is not with any of the oob steps.
My question is do you need to actually open or click on the tab? You should be able to set and assert values in fields on a different tab than the active tab. What exactly are you trying to do by clicking on another tab? If you just need to see it in a screenshot or something like that you might try turning off Tabbed Forms for your ATF user so that the form is just one long page.
