Make sure that you're using the same workgroup name (e.g. "Workgroup") for all the computers. Assuming that you don't have any Windows NT/2000 servers running all your computers must be set to use workgroup instead of domain. If you still have problems try doing the following for the W98 PCs that are slow in seeing the W2K machine:
1)in a DOS window, type "edit c:you_windows_directory(usually "windows")hosts
2)type "name of your W2K computer", tab, and then its IP address. E.g.
mywin2K 192.168.100.5
3)save the file and exit
Now see if the problem is fixed- no reboot necessary.
David