Bandwidth issue on Windows Server 2003

Hi,

I am experiencing a very weird problem. I have a Windows Server 2003 Std
Edition connected to a 100Mbs internet connection in a datacenter.
Alongside this box there 3 other boxes on the same subnet : 2x Linux and
1x identical Windows box.
Here are the bandwidth figures I get :

Windows -> outside PC with 2Mbit/s ADSL connection : 1200kbit/s (HTTP)
and 550kbit/s (FTP)
Windows -> outside PC with 1,6Mbit/s ADSL connection : 960kbit/s (HTTP)
and 400kbit/s (FTP)
Linux -> outside PC with 2Mbit/s ADSL connection : 2Mbit/s (HTTP) and
2Mbit/s (FTP)
Linux -> outside PC with 1.6Mbit/s ADSL connection : 1.6Mbit/s (HTTP)
and 1.6Mbit/s (FTP)
Windows -> Linux : 30Mbit/s
Windows -> Windows : 30Mbit/s
Linux -> Linux : 65Mbit/s

So there obviously is a problem with the Windows servers and I think it
could be related to TCP/IP settings. I tried changing the
EnablePMTUDiscovery and TcpWindowSize but without any noticeable change.

If I start two downloads on the Windows server from a single 2Mbit/s
ADSL connection, I get 1Mbit/s for each download. This way I was able to
get 3 fast ADSL connections to download a total of 6Mbit/s from the
Windows server. This should show it's not a simple bandwidth problem.

The Linux servers show the connection is ok and for some reason, the two
Windows servers are not taking full advantage of it.

I was able to test the following protocols : HTTP (Abyss Web Server),
FTP (FileZilla Server) and MMS (Windows Media Services). None of them
can fill up the full bandwidth, but HTTP and MMS can achieve
significantly faster downloads than FTP.

From the operator's point of view, 2 out of 3 routers have been changed
in the last 2 months and the problem is still here. The last router
serves many other Windows and other OS's and none of them show this problem.

Here is some background information :

- this issue happenned on two different boxes, with same hardware
(SuperMicro P4SCI with two gigabit controllers : 1x Intel 82547GI CSA
and 1x Intel 82541)
- the two boxes are in the same datacenter with a connection at least
100Mbs (the boxes are 100Mbs wired)
- the boxes are running Windows Server 2003 Standard Edition. The
problem starts to show with no additional software or configuration,
straight after Windows installation.

Does anyone see a solution to this problem ? Should I give more
information ?

Thanks a lot !

Dario Spagnolo