Win 2003 R2 x64 slow network performance SMB/CIFS

Hi everyone, i've got a problem with a brand new HP dl360 g5 quad core with 8
Gb of RAM and windows 2003 server R2 x64 std, from which i can download files
only at 5 Mbit per second or so...

I have a NIC and a Switch Gigabit.

On the same switch there are other 7 servers (but 32bit). With those NO
PROBLEM.

No Problem Between all servers.
No problem Between clients and 32 bit servers.

The problem occurs only between my clients and THAT SPECIFIC server.

I tried to:

-disable antivirus
-set negotiation to 100 Full.
-change cable
-change port on the switch (using one of those that works for 32 bit servers)
-Install the patch described in the KB 925511 ( but it says: the service
pack version of this system is newer .... )


Other data:

-NIC is onboard HP GB standard.
-There are NO NLB, Fault Tolerant or stuff like that neither on the
server/card nor in the net
-there are NO significant quantity of packet collisions nor packets dropped
-in the system monitor you can see that there is a constant download speed.

any ideas?

Thanks in advance


Diego Castelli