Network browsing takes ages when one computer is declared as Internet zone on a 4-computer network

I've a small network made of 3 computers plus an additional one, the guest, connected time to time (IP address 192.168.0.100). I configured ZA to consider this address as belonging to an Internet Zone. The other PCs have of course a fixed address, resp. 192.168.0.10,

The Internet connection sharing works well from everywhere (an USB ADSL modem is connected to a gateway running Win98SE).

But the windows file explorer doesn't recognize any network when this guest's PC is connected. In the same time I can copy files from one computer to another one with batch files, giving the full link : copy \\\\computer_1\\source_dir\\source_file.ext" "E:\\target_dir\\target_file.ext".

Somebody can explain ? Thanks