What you do depends on whether you want a dashboard (as in the generic term for a group of related charts) or a Dashboard (as in the Visualization API object that handles binding charts and controls together). In the former case, you can do something like this:
http://jsfiddle.net/asgallant/Xfx3h/, in the latter, something like this:
http://jsfiddle.net/asgallant/Kuyr6/
The latter example is far more complicated than necessary to demonstrate the point, but it happens to be something I'm currently working on as a side project.