Network Browser to Slow on New Server with win2k3...?

Hi guys, i have one great problem with our new server, is a great system but
went i browse my network takes more time than the average of my other systems.

This new server is:
SuperMicro SYS7044H-82R
2GB RAM
1 CPU 3GHZ
Raid-5 4-disk SCSI
2 NIC's 1GB

Is really faster working locally, programs etc, but went i try to browse
my domains the performance is bad , almost 10 seconds to show me the
clients, to much delay, if i try to browse that system with other system,
some times give me back the pop-up saying "is not accessible or that i dont
have permission to use this network resource...", i already re-install win2k3
std edi. 3 times, because is not giving me the performance i need. I plug-in
to my swith them to my router, it has the option to change the speed:

First time was automatic
Right now is 100/100Mb Full-Duplex

I have a lot of options for this driver to play with but, iam here trying
to get some tips, my switch model work at 100Mb Full Duplex, i setup 2
machines with win 2k3, this one and other to test.

My test machine is really cool, is working very very good, my browser
average are what i need, my clients logins are fast, both system are on the
same sub-net 192.168.2.X, on that i have 3 domains:

A) The production is working with NT 4 100Mb NIC
B) The test with win2k3 100Mb NIC AMD 1.6GHZ 512RAM
C) The New with win2k3 1Gb NIC

*The three system have static IP's.
*The win2k3 has all the patches
*My Network is working at 100Mb
*Switch Baystack
*Event Viewer dosent have any error about.

System A and System B have great performance browsing the network, but
the C is to slow. Some times went i ping the IP i lost packages, i was
thinking that maybe the speed of the NIC are more faster than my network and
my equipment is not handling very well the comunication.

I install the latest drivers from windows update, the nics are

Intel® 82546GB Dual-port Gigabit
Ethernet Controller

This performance is on both types, working like workgroup or domain.

I try to install one PCI NIC 100Mb, but i dont that slot any more, i have
only two more things to do:

1; Play with the NIC's options
3; Setup AD+DNS manuallyn some book say that sometimes the wizard make
mistakes.
2; Re-install win2k3, dont install any patch and see the performance .

Any tips or information about i will apreciate , thanks all for your
time, and great day to all.