New Win7 not playing nice on LAN

3 XP computers on LAN. Added new Win 7. All can access the Internet. All can ping the router. The router can ping all PCs. All XPs share files OK with other XPs. All have Network Discovery enabled. LLTD is enabled on all. Norton Protection Center on all. All are part of the same workgroup and on the same network. When I look at the Network Map Win 7 it only has itself as a computer. I can map \\someXP\somefile on the Win7. I can also see [someXP] as a media server on Win7 network map. Win7 can ping all media devices but not any computers on the LAN. Browse network from Win7 doesn't show any XPs. XPs cannot ping Win7 or see Win7 on network browse. Norton network discovers all LAN connected devices/computers both on Win7 and XP computers. All are set to Full Trust. Turning off Norton Firewall gives no joy. No Homegroup on Win7 - set to Work Network. I would like to see these XP machines on the net from Win7. Any ideas?