Install via http proxy

[Bastiaan Naber <bastiaan@ricardis.tudelft.nl>]

Hi, 

I am trying to get debian amd64 installed for the first time. On my previous 
dual opteron I installed gentoo but since debian in my preferred OS want 
debian on this one. It is going to be used as a mysql database server.

I am on a local network on which one machine runs a http proxy. Normaly I 
install the base system and do:

export http_proxy=...:8888 

and then I can do dselect etc...

I downloaded the net install and installed it, it worked great. I now have a 
system which I want to update. I have a local network connection and I did 
the export after which I can get internet pages with wget, so I have a 
connection to the internet. However when I start dselect and try to do an 
update it refuses and says it can't connect to the alioth site.

My source.list:

deb http://debian-amd64.alioth.debian.org/pure64 sid main

Can anyone help me here ? I normaly install all my machines (10+) like this 
and this hasn't been a problem sofar.

Thanks for your help,
Bastiaan