Proliant ML330 Stopped Talking to Dell Servers

[Chris Cunningham_1]

I run two dell poweredge servers and a proliant ml330 server on my DMZ, one dell server is our primary webserver hosting Coldfusion 5 on windows Server. The other is our DB Server running MS SQL 2000. The compaq runs a scheduled tasks and is a mail gateway for virus scanning using Trend Micros MSS for NT.
About 2 days ago the compaq server stopped responding to any network traffic going to or from the webserver. In the event logs it mentioned that there was a conflict with the netbios name as there was a duplicate on the network. (this is strange as there has been no changes to the network or servers in over two months, since the last reboot of the webserver.)
After rebooting the proliant serval times the I stopped recieving the error regarding NetBT and it appeared to boot normally. except we still cannot see the webserver even tho they are plug into the same switch.
I installed another NIC into the proliant (a simple 3com card) and set that up exactly the same as the other NIC in the server, and it had no problems connecting to the webserver.
With this I contacted Compaq who sent a engineer out today with a new video, raid and network combo card and replaced it. we replaced the card and removed the NIC that i had put in there and we still had the same problem. we reinstalled the drivers, updated the drivers, we even went so far as to completly change the name of the server to something_else.
We know that both servers can see each other as both can get each others Mac addresses when we do a arp -a command.

Does anyone have any idea on what could solve this other than keeping the 3com network card in it?

Thanks in Advance!
Cheers Chris