[X4U] problem getting online

[Michel Treisman]

I have a 17" AlBook which I have just upgraded to 10.4.5 - but that's  
not the issue, I had the problem (see below) on 10.4.4 too.

I use a netgear DG834G router to go online. When I am at my desk I  
plug  the ethernet cable into the AlBook and turn Airport Off.
When I am elsewhere I use wi-fi.
At my desk, using built-in ethernet, the internet disappears at  
arbitrary times: I get the message "You are not connected to the  
internet".

So I open System preferences/Network and it tells me that I am using  
DHCP.  But the IP Address, Subnet Mask, etc have disappeared.
I click 'Renew DHCP lease' but it does me no good at all.

The puzzle is, if I now turn Airport On,  I am on the internet again.  
Turn Airport Off, built-in ethernet is not working.

So I put a Pismo on  my desk, side-by-side with the AlBook. If the  
AlBook tells me  "You are not connected to the internet" I switch the  
ethernet cable to the Pismo. No problem now! the Pismo is on the  
internet.

Suddenly, after up to 60 min of this kerfaffle, Network Preferences/ 
Built-in Ethernet fills  up  with my IP Address, Subnet Mask, etc,  
and I am online again and the problem is over.

The problem can't be the router - it works with the Pismo.  There is  
no problem with wi-fi that I can't handle by turning Airport Off and  
On again.

So what should I do next?

Mike