why cannot see neighbors easily

I’ve set up a LAN in the company, around 30 clients and 1 server. The clients have Win2000pro, WinXP, Win98, and various OS. The server use Win2000 Adv Server system.
Now the clients cannot see their neighbors in “My Network Places”. But they can access neighbors’ resources by running “\\host name or IP address”. Anyhow, colleagues feel this not convenient.
What is the problem point? How can clients see all their neighbors easily in “My Network Places”?