We had a problem on our network when we mixed 3Com NICs with IBM NICs on a token ring system. The 3Com cards would send false signals [beacon] to the server and bring it down. I would suggest switching NICs first. Tha is a fairly cheap test.

>Hi all,
>
>I have a friend who's having a little trouble and I suggested that one of the braniacs *g* here might be able to help out. Here's Mark's email message to me:
>
>Doug,
>
>It was nice to talk with you last night. Thanks for the offer to post my network problem to levelextreme.com. Here it is:
>
>I have a network consisting of three machines: An AMD K6-2 300 MHz running
>Windows NT Server 4 (SP 5) and Small Business Server, A Pentium II 300 MHz
>running Windows NT Workstation 4 (SP 5) and a Pentium 133 MHz running
>Windows 98 (originally running Second Edition, but now running the original
>release of 98). The NT Server provides a DCHP server.
>
>The machines were originally connected using coax and some old NE2000
>compatible ISA network cards. The network between the two NT machines has
>been running very well for several months as long as the Windows 98 machine
>was not powered on. However, if the Windows 98 machine was powered up, I
>would sometimes get the NT Workstation machine to lock up tight (requiring a
>hardware reset). I attribute this to something related to the network cards.
>However, if I had just the Windows 98 machine and the NT server running,
>everything seemed to work okay i.e. no lock ups.
>
>I recently upgraded my network cards to 100 base-T. The NT Server and the
>NT Workstation have 3Com 3C509B PCI cards. The Windows 98 machine has a
>RealTek 8139 PCI card.
>
>The NT Workstation machine works fine. However, the Windows 98 machine is
>unable to get an IP address from the DCHP server on the NT Server. If I set
>it up for a hard configured IP address, it works on the network just fine.
>It also seems, (although I don't have a lot of history yet) that having the
>Windows 98 machine, no longer locks up the NT Workstation.
>
>If the Windows 98 machine doesn't have a hard configured IP address, it uses
>an autoconfigure IP address. If I disable autoconfigure IP address, it gets
>and address of 0.0.0.0. When the Windows 98 machine uses an autoconfigure
>IP address, it can't communicate with the rest of the network.
>
>I have tried with no success removing all the network adapters, clients and
>protocols and reinstalling and doing a complete reinstall (FDISK and format)
>of Windows 98, this time with the original version.
>
>The activity lights on my hub indicate a 100 Base-T connection to all
>machines. I have also verified the integrity of all the cabling with a cable
>tester. The Realtek diagnostic says the card is okay, although I didn't
>attempt a network or loopback test.
>
>I attempted to examine the DCHP server log on the NT server, but it doesn't
>show any activity, even though I know the NT workstation is getting
>addresses and logging is enabled.
>
>This probably isn't a major issue as I can just assign a fixed address to
>the Windows 98 machine and I don't use that machine as much as the other
>two.
>
>Thanks,
>Mark