Machine2 is Windows 2000 SP4. Machine1 is XP Pro SP2 with the firewall disabled. Both machines are on the same subnet behind a Netgear wired router.
When admin1 is logged into Machine2, she can browse the Windows Network ("Computers Near Me") and see Machine1, along with its shared printers and folders. When admin2 is logged into the same machine, Machine2, Machine1 does not show up anywhere in browsing, even after a long wait. She can reach Machine1 with Start | Run "\\Machine1", but she cannot browse there.
The reason that this is a problem is that there is an application that admin2 needs to run that needs to access a folder on Machine1. The application does not allow typing in the UNC path. The folder has to be selected by browsing to Machine1 from Machine2.
Remember, everything is perfect until admin1 logs out of Machine2 and then logs in as admin2. Therefore, the cabling, jacks, NICs, and the like are all fine. Neither machine has any spyware or viruses. (We used to have this problem all the time in Windows 98, but not in 2000/XP.)
I just did a temporary work around by mapping a drive letter on Machine2 to Machine1. (I was able to access the folder by typing in the UNC.) Even then, though, Machine1 still does not show up in Computers Near Me or Network Neighborhood. I'd like to solve the browsing problem, it it can be done. The situation is as if the XP machine is not announcing itself to the network, but that cannot be the problem since everything works fine when admin1 is logged in.