From: "Rich Gauszka" 


http://www.neillans.co.uk/?p=165
Heres the fix (well, this worked for me).

This problem existed in RC1 and to some extent RC2 too. I did report it,
and it's partially fixed but still not good. Microsoft at the time blamed
my Cisco router.. Anyway, I get really poor intermittant network
performance. It turns out this is due to a new addition in the TCP/IP stack
called Receive Window Auto-Tuning Level.

To check the status of this feature, run "netsh interface tcp show
global" at a command prompt.

You will see something like:

Querying active state.

TCP Global Parameters
----------------
Receive-Side Scaling State : enabled Chimney Offload State : enabled
Receive Window Auto-Tuning Level : disabled Add-On Congestion Control
Provider : none ECN Capability : disabled
RFC 1323 Timestamps : disabled

In this example, you can see I have it disabled. (My network performance
returns to normal with it off!).
To disable it, run: "netsh interface tcp set global
autotuning=disabled" To enable it, run: "netsh interface tcp set
global autotuning=normal" (Both these last two should be run from an
Administrator Command Prompt, not a "normal" command prompt).

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