This dashboard control enables you to list all members in one or more Member Groups. The dashboard control will be available within the Umbraco client dashboard as a control in the members section (if you choose to install it there - see below).
Download and install the package as usual - from the Umbraco backend developer section.
I just packaged it up as a real package recently, so please let me know if you encounter any problems installing it.
NOTE: Check out the Blackpoint Member Admin package (http://our.umbraco.org/projects/backoffice-extensions/blackpoint-member-admin) embedding this functionality.