Weird mirrors error on fresh Lenny installation

[Lisi <lisi.reisz@gmail.com>]

This morning I installed Lenny using netinstall.  I have done this with Debian 
many times over the years without problem.

I always install the base system, let the standard system be set up 
automatically and then install anything else I want manually after rebooting.  
Today, that didn't work.

The mirrors are said to be uncontactable and the reason is given as 101 
network unreachable.

I have checked everything.  The router is working fine (I have had a look and 
reset everything).  The system is being given a DHCP address - I check with 
ifconfig.  I can ping the router by IP and Google by url.  I have tried 
editing the network interfaces file and setting it up for static IP.  It made 
no difference.  I have tried 3 different mirrors - *ox.ac.uk*, *man.ac.uk* 
and the primary UK mirror.  The system still reports failure, both when it 
tries to verify the security and volatile sources and when accessing the 
mirrors - but it installs the standard system without any other hitch.

In desperation I did a fresh installation.  Same problems.  I am out of 
ideas - can anyone suggest anything??

TIA,
Lisi