cannot access www via a proxy while in a VPN

[Steve S <elcorto@gmx.net>]

Hi

I'm starting a VPN with the network of my university via vpnc. The VPN itself
seems OK. I can ssh directly into machines at the university and ifconfig
says

[...]
tun0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          inet addr:139.20.208.209  P-t-P:139.20.208.209  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1412  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
[...]

Now, while in the VPN, to go from my machine to the net (I need a
university IP to access certain services), I need to go over their www
proxy. I entered the proxy in iceweasel, but it's just "Waiting for
www.google.com ...". No connection either with lynx/w3m

    HTTP_PROXY="http://www.example.com:80"; w3m www.google.com
    -> www.google.com contacted. Waiting for reply...
    http_proxy="http://www.example.com:80"; lynx www.google.com
    -> HTTP request sent; waiting for response.

I know that it worked with an older system (lenny) and it works now with
Window$, the Cisco VPN client and Firefox 3, so I figure that it's
definitely my current installation. I'm using Gnome, so I also tried
with the (new) NetworkManager deactivated, but to no avail.  My machine
is connected to a hardware router, but with no special firewall settings
there. Also, I didn't change the router's config for a long time, so
it's setup is identical to the one I used with my older install.

I'm running testing, 2.6.24-1-486 (Debian 2.6.24-7), 
vpnc 0.5.1r334-1 .

I'll appreciate any tips on how to test this setup further.

TIA!

best,
steve