Problem with KPackageKit update

[schrod at biochem.mpg.de]

Dear all,

I recently installed Kubuntu on my work computer, which sits behind a  
proxy server. I set the proxy settings in the system settings/network  
as well as in the .bashrc and it seems to work (ping in the terminal  
and web browsing via konqueror).

However I have a severe problem. When I want to install new packages,  
KPackageKit does not find anything. I thus want to refresh my  
repositories. I go to settings --> edit software sourses and  
uncheck/recheck one of the repositories. When I close the window, it  
tells me I have to reload. I confirm and it starts downloading.
The problem: it always stops at 25% (or sometimes 27% or 28%),  
independent of which repositories are checked!?

What can I do?

I tried to sudo apt-get update from the terminal, but it complains it  
can't connect to the server. However if i ping the server, I get a  
response.

Thanks for any advice, as I am pretty unfamiliar with ubuntu/kubuntu.

Nikolas