Freezing or stalling current system

I first tought is was because I was trying to get to run a kernel under 
XEN on Ubuntu, but now I have the same problem on a spare dual opteron 
system....

What happens is that the system runs for a while especially if the 
network is not connected. The network on the opteron is a bge 5705 
onboard chip. XEN uses the xn0 xen-device.

Once the network is fired up it does not take too long for the system to 
"Freeze".

On the XEN system I could get thing running again most of the time by 
just pressing ^T. That would get packets reflowing.
I'm using nfs/tcp mounted disks and rsync.

On the opteron system things are a little harder to get it revived.
- Some of the freezes are hard. Can't break into the debugger with the 
keyboard. Left the system over night,but it never got back to live.
- Some of the freezes are not real freezes but things just stall for a 
while and then continue again....
- Some freezes let me allow to break into the debugger, and then just 
going 'cont' gets the things going for a short while.

I'm sort of assuming that the bge0: timeouts and coalesced links are due 
to the freezing.

So my very amature conclussion is that things are "deadlocked" 
somewhere. But I need some guidance to be able to give more usefull 
info. I anyone wants to hold my hand, I'll set it up with a serial 
console and hook it up to another system for easier logging.

--WjW