Workgroups on differnet logical networks

I have a router w/ 3 LAN interfaces, 3 different logical network address spaces.
On every logical network there are some xp stations and all of them belong to the same workgoup. All pc have installed serv. file & print share, microsoft net clients.

When I brouse “my networkplaces” I see only the router and the local pc. How can I see pcs from other logical networks?
NOte” ALL pcs can ping each other by ip or pc name.