I'm not sure what recently happened, but here's the thing.
I have a home network, 1 Vista desktop, 1 XP desktop with Shared USB drive attached, 1 NAS drive (running linux kernal I believe). All devices set to same workgroup "HOME". Until recently, I could see all devices from the Vista machine with the explorer "network" selection.
Now I can only see myself, the wireless router, and if I turn it on, another Vista laptop.
I can connect to the XP computer manually by entering \\computer_name\external_drive_name and the same with the NAS drive. I just can't see them with Vista explorer.
FYI - Norton 365's security map option also shows everything on the network so I know all devices are in the same workgroup.