Computes lost in Network Neighborhood

I have a two computer network. One using WME and one using W98. They are connected with a cross over cable. When first turned on, they see one another and can share. After a little while, you click on Network Neighborhood they are gone. The customer re-booted and they re-appeard. Customer did not know to hit F5 to refresh. I instruced them to do this next time and see if they re-appear without re-booting. What can I do to prevent the computers from disappearing?

Thanks
Selina