i have exactly same problem, looking for a solution
i'm using ubuntu 10.04 and these are what i tried so far.
i added my proxy adress, port, user and password by using gui (System->Preferences->Network Proxy->Manual)
i tried to export http_proxy, https_proxy on terminal by using correct proxy definition.
Also i had firefox, google chrome and opera.
interestingly, just firefox can accces internet if i configure to use manual settings in firefox.
All the way, the result always 407.
Any help would be appreciated
