Peer to Peer browsing

Have 3 XP PCs. A & C can ‘see’ each other neither can see B. All can ping another all can browse through the gateway. If IPX is enabled B becomes accessible. Guest a/c is enabled. Local sec policy is identical. Registry hacked so only A is master browser. All belong to same workgroup. On B makes no diff if using Ethernet or WiFi adaptor.
If booting B to Win2K all is OK.
Any further ideas?