Just a quick post on how I managed to get my Ubuntu Software Center working at work where I had a proxy between me and the Internet which required username and password authentication.
Now really this should have not been an issue I think, since there’s a “Network Proxy” setting in the “Preferences” for Ubuntu but for some reason the Ubuntu Software Center doesn’t seem to take note of this (or the authentication details for username and password at least).
So anyway, this is how I got it working through a proxy on my 11.04 Ubuntu. Basically you need to edit the /etc/apt/apt.conf file with a line like the following and replacing user, pass, host and port with the relevant dertails.
Hope this helps.