Forwarding messages.

I have a very strange problem. I manage a peer-to peer mixed environment. Seven of the machines are Win98SE, one NT4 (sp5), six W2kPro (fat32) and my W2kPro (NTFS). The problem comes when the Win98 PC’s attempt to forward, reply to or send attachments using Outlook Express or Outlook 2000. When My W2K machine is on they cannot execute these commands, however, when my machine is off the problem goes away.
I suspect that there is a master browser issue going on but I am unable to determine what it might be. I am running IIS as well.
Any help out there?