The other day, I had asked plugin developers to dish out their wish list for the plugin repository. Olivier published a comment recommending a plugin called WATS or WordPress Advanced Ticketing System as a way of handling support on your own website.
After installation, users need to visit the Wats Options page within the Settings

More at: http://weblogtoolscollection.com/archives/2010/01/29/plugin-review-wordpress-advanced-ticket-system/